Sample records for pvdf membrane pores

This paper deals with bimetallic (Fe/Pd) nanoparticle synthesis inside the membranepores and application for catalytic dechlorination of toxic organic compounds form aqueous streams. Membranes have been used as platforms for nanoparticle synthesis in order to reduce the agglomeration, encountered in solution phase synthesis which leads to a dramatic loss of reactivity. The membrane support, polyvinylidene fluoride (PVDF) was modified by in situ polymerization of acrylic acid in aqueous phase. Subsequent steps included ion exchange with Fe2+, reduction to Fe0 with sodium borohydride and Pd deposition. Various techniques, such as STEM, EDX, FTIR and permeability measurements, were used for membrane characterization and showed that bimetallic (Fe/Pd) nanoparticles with an average size of 20-30 nm have been incorporated inside of the PAA-coated membranepores. The Fe/Pd–modified membranes showed a high reactivity toward a model compound, 2, 2′-dichlorobyphenyl and a strong dependence of degradation on Pd (hydrogenation catalyst) content. The use of convective flow substantially reduces the degradation time: 43% conversion of dichlorobiphenyl to biphenyl can be achieved in less than 40 s residence time. Another important aspect is the ability to regenerate and reuse the Fe/Pd bimetallic systems by washing with a solution of sodium borohydride, because the iron becomes inactivated (corroded) as the dechlorination reaction proceeds. PMID:20161475

Four common types of additives for polymer membrane preparation including organic macromolecule and micromolecule additives, inorganic salts and acids, and the strong non-solvent H2O were used to prepare poly (vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) hydrophobic flat-sheet membranes. Membrane properties including morphology, porosity, hydrophobicity, pore size and pore distribution were investigated, and the permeability was evaluated via direct contact membrane distillation (DCMD) of 3.5g/L NaCl solution in a DCMD configuration. Both inorganic and organic micromolecule additives were found to slightly influence membrane hydrophobicity. Polyethylene glycol (PEG), organic acids, LiCl, MgCl2, and LiCl/H2O mixtures were proved to be effective additives to PVDF-CTFE membranes due to their pore-controlling effects and the capacity to improve the properties and performance of the resultant membranes. The occurrence of a pre-gelation process showed that when organic and inorganic micromolecules were added to PVDF-CTFE solution, the resultant membranes presented a high interconnectivity structure. The membrane prepared with dibutyl phthalate (DBP) showed a nonporous surface and symmetrical cross-section. When H2O and LiCl/H2O mixtures were also used as additives, they were beneficial for solid-liquid demixing, especially when LiCl/H2O mixed additives were used. The membrane prepared with 5% LiCl+2% H2O achieved a flux of 24.53kg/(m(2)·hr) with 99.98% salt rejection. This study is expected to offer a reference not only for PVDF-CTFE membrane preparation but also for other polymer membranes. PMID:27372116

In this study, the polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were prepared by non-solvent induced phase separation (NIPS). The influences of PVDFmembrane thickness and polyethylene glycol (PEG) content on membrane morphologies, pore size, mechanical and permeable performance were investigated. It was found that membrane thickness and PEG content affected both the structure and performance of hollow fiber membranes. The tensile strength and rejection of bovine serum albumin (BSA) increased with increasing membrane thickness, while the Ultrafiltration flux (UF) flux of pure water was the opposite. The tensile strength, porosity and rejection of BSA increased with increasing PEG content within a certain range. Compared with commercial F60S membrane, the PVDF hollow fiber membrane showed higher mechanical and permeable performance. It was proven that PVDF material had better hydrophilicity and lower BSA adsorption, which was more suitable for hemodialysis. All the results indicate that PVDF hollow fiber membrane is promising as a hemodialysis membrane. PMID:24957122

In this study, the polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were prepared by non-solvent induced phase separation (NIPS). The influences of PVDFmembrane thickness and polyethylene glycol (PEG) content on membrane morphologies, pore size, mechanical and permeable performance were investigated. It was found that membrane thickness and PEG content affected both the structure and performance of hollow fiber membranes. The tensile strength and rejection of bovine serum albumin (BSA) increased with increasing membrane thickness, while the Ultrafiltration flux (UF) flux of pure water was the opposite. The tensile strength, porosity and rejection of BSA increased with increasing PEG content within a certain range. Compared with commercial F60S membrane, the PVDF hollow fiber membrane showed higher mechanical and permeable performance. It was proven that PVDF material had better hydrophilicity and lower BSA adsorption, which was more suitable for hemodialysis. All the results indicate that PVDF hollow fiber membrane is promising as a hemodialysis membrane. PMID:24957122

The TiO2 nanoparticles entrapped poly(vinylidenefluoride) (PVDF) hybrid membranes were prepared through impregnating the pre-treated PVDF film in the TiO2 suspension. SEM, XRD, TG and ATR-IR analyses were used to character the hybrid membranes. The results showed that the TiO2 nanoparticles with average size about 44 nm were deposited on the surface and inner pores of PVDF films. The pre-treatment of PVDF with cetyltrimethyl ammonium bromide (CTAB) is benefit for TiO2loading. The ATR-IR spectra revealed that physical interaction played important role in the construction of hybrid membranes. The adsorption behavior of Cu2+ on the hybrid membranes was studied, and a promoted adsorption and elution efficiency of PVDF/TiO2 hybrid membranes were observed compared with that of the pristine PVDF film. Meanwhile, the surface contact angle, pure water flux and static adsorption of bovine serum albumin (BSA) on the hybrid membranes were also measured to study the effects of TiO2 nanoparticles. It was found that the TiO2 nanoparticles improved the surface hydrophilicity and permeability of PVDFmembranes, and the decreasing adsorption capacity of BSA indicated the promoted antifouling ability of PVDFmembranes. Such the PVDF/TiO2 hybrid membranes exhibit potential applications in the separation and pre-concentration of metal ions.

Polyvinylidene fluoride (PVDF) membranes were exposed vertically to a high energy electron beam (EB) in air, at room temperature. The chemical changes were examined by Fourier Transform Infrared Spectroscopy (FTIR). The surface morphologies were studied by Scanning Electron Microscopy (SEM) and showed some changes in the pore size. Thermogravimetric (TGA) analysis represented an increase in the thermal stability of PVDF due to irradiation. Electron paramagnetic resonance (EPR) showed the presence of free radicals in the irradiated PVDF. The effect of EB irradiation on the electrical properties of the membranes was analyzed in order to determine the dielectric constant, and an increase in the dielectric constant was found on increasing the dose. The surface hydrophilicity of the modified membrane was characterized by water contact angle measurement. The contact angle decreased compared to the original angle, indicating an improvement of surface hydrophilicity. Filtration results also showed that the pure water flux (PWF) of the modified membrane was lower than that of the unirradiated membrane. PMID:25569360

Polyvinylidene fluoride (PVDF) membranes were exposed vertically to a high energy electron beam (EB) in air, at room temperature. The chemical changes were examined by Fourier Transform Infrared Spectroscopy (FTIR). The surface morphologies were studied by Scanning Electron Microscopy (SEM) and showed some changes in the pore size. Thermogravimetric (TGA) analysis represented an increase in the thermal stability of PVDF due to irradiation. Electron paramagnetic resonance (EPR) showed the presence of free radicals in the irradiated PVDF. The effect of EB irradiation on the electrical properties of the membranes was analyzed in order to determine the dielectric constant, and an increase in the dielectric constant was found on increasing the dose. The surface hydrophilicity of the modified membrane was characterized by water contact angle measurement. The contact angle decreased compared to the original angle, indicating an improvement of surface hydrophilicity. Filtration results also showed that the pure water flux (PWF) of the modified membrane was lower than that of the unirradiated membrane. PMID:25569360

Polyvinylidene flouride (PVDF) membranes supported on non-woven fabrics (NWF) of polyester are reported. The PVDFmembranes were fabricated using the phase inversion method followed by modification of the active top layer of the PVDF thin film by adding polyvinylpyrolidone (PVP) into the cast solution. A PVDF resin was used with N- methyl-2-pyrrolidone (NMP) as a solvent. Sessile drop contact angle measurements and scanning electron microscopy (SEM) were used to study the physical properties of the membranes. Membrane rejection of humic acid was studied using a cross-flow membrane testing unit. The contact angle results revealed that the hydrophilicity of PVDFmembranes increased as the PVP concentration was increased from 3 to 10 wt%. SEM analysis of the membranes revealed that the membranepore sizes increased when PVP was added. AFM analysis also showed that membrane roughness changed when PVP was added. Total organic carbon (TOC) analysis of water samples spiked with humic acid was performed to test the rejection capacity of the membranes. Rejections of up to 97% were achieved for PVDFmembranes supported on polyester NWF1, which had smaller thickness and higher permeability compared to polyester NWF2. The NWFs provided the high strength required for the membranes despite the modifications done on the PDVF surface and microstructure.

Polyvinylidene fluoride (PVDF) ultrafiltration membranes were investigated for the first time in vanadium redox flow battery (VFB) applications. Surprisingly, PVDF ultrafiltration membranes with hydrophobic pore walls and relatively large pore sizes of several tens of nanometers proved able to separate vanadium ions and protons efficiently, thus being suitable as a VFB separator. The ion selectivity of this new type of VFB membrane could be tuned readily by controlling the membrane morphology via changes in the composition of the membrane casting solution, and the casting thickness. The results showed that the PVDFmembranes offered good performances and excellent stability in VFB applications, where it could, performance-wise, truly substitute Nafion in VFB applications, but at a much lower cost. PMID:23223708

This study proposes a method to prepare a crack-free poly(vinylidene fluoride) (PVDF) microfiltration (MF) membrane with enhanced antifouling property. In the study, blending 4% poly(vinylidene fluoride)-graft-poly(sulfopropyl methacrylate) (PVDF-g-PSPMA) and 1.5% potassium perchlorate (KClO4) led to crack prevention during membrane preparation via nonsolvent induced phase separation (NIPS) when compared with blending with 4% PVDF-g-PSPMA only (without KClO4). The resulting crack-free membrane (A3) had both smooth surface structure and hydrophilicity in comparison with pristine PVDFmembrane (A1). In addition, blending with PVDF-g-PSPMA and KClO4 also allowed the A3 membrane to exhibit uniform pore size distribution (PSD) and smooth surface structure, compared with PVDFmembrane commercially available from company "M" in Germany. The aforementioned properties led to antifouling characteristics in the crack-free membrane (A3). According to flux performances, flux recovery and cumulative permeate volume (between 120 and 240 min) of crack-free membrane (A3) were 11.41 and 17.41% superior to those of commercial membrane, respectively. PMID:26172403

This contribution demonstrates a method for PVDF microporous membrane modification via surface-initiated activators generated by electron transfer atom transfer radical polymerization (AGET ATRP) directly from the membrane surface. Three hydrophilic polymers, poly(2-(N,N-dimethylamino) ethyl methacrylate) (PDMAEMA), poly(2-oligo (ethylene glycol) monomethyl ether methacrylate) (POEGMA), and poly(2-hydroxyethyl methacrylate) (PHEMA), were grafted from the PVDFmembrane surface in aqueous solution at room temperature. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the successful covalent tethering of the polymer chains onto the PVDFmembrane surface. The gravimetry results indicated an approximately linear increase of the graft yields, up to about 330 μg/cm 2 for DMAEMA and 470 μg/cm 2 for both HEMA and OEGMA, with the polymerization time. Block copolymer brushes were prepared by chain extension. Water contact angle decreased over 50% for high yields, indicating improved surface hydrophilicity. The effects of the graft polymerization on membrane surface morphology, pore structure and permeability were investigated. It was found that the surface roughness was decreased and the pore size distribution was narrowed. The membrane permeability increased at low graft yields due to the enhanced hydrophilicity and decreased at high graft yields due to the overall reduction of the pore diameters.

Membrane distillation (MD) is a promising separation technique capable of being used in the desalination of marine and brackish water. Poly(vinylidene fluoride) (PVDF) flat sheet nano-composite membranes were surface modified by coating with electro-spun PVDF nano-fibres to increase the surface hydrophobicity. For this purpose, the nano-composite membrane containing 7 wt.% superhydrophobic SiO2 nano-particles, which showed the highest flux in our previous work, was first subjected to pore size augmentation by increasing the concentration of the pore forming agent (Di-ionized water). Then, the prepared flat sheet membranes were subjected to nanofibres coating by electro-spinning. The uncoated and coated composite fabricated membranes were characterized using contact angle, liquid entry pressure of water, and scanning electron microscopy. The membranes were further tested for 6 h desalination by direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD), with a 3.5 wt.% synthetic NaClaq as the feed. In DCMD the feed liquid and permeate side temperature were maintained at 27.5 °C and 15 °C, respectively. For VMD, the feed liquid temperature was 27 °C and a vacuum of 94.8 kPa was applied on the permeate side. The maximum permeate flux achieved was 3.2 kg/m(2).h for VMD and 6.5 kg/m(2).h for DCMD. The salt rejection obtained was higher than 99.98%. The coated membranes showed a more stable flux than the uncoated membranes indicating that the double layered membranes have great potential in solving the pore wetting problem in MD. PMID:26630042

Production of porous membranes using heavy ion bombardment and subsequent chemical etching of poly(vinylidene difluoride) (PVDF) films has been reported several years ago. However, porous membranes with pore diameter in the nanometer scale requires a better understanding of the chemical etching mechanism. In this work PVDF foils irradiated with Sn ions (2.85 MeV per nucleon) were exposed to several etching conditions which involved permanganate oxidation in different alkaline environments. The solution of KOH 9 mol L-1 and saturated in KMnO4 was the best etching reactant for PVDF. Functional groups created in the alkaline and oxidative attack by permanganate were studied by FT-IR and UV-vis spectroscopy. The spectroscopic data reveals that the formation of pores occurs by a two-step mechanism: (i) double bonds as a result of dehydrofluorination induced by alkaline media and (ii) oxidation of these double bonds in permanganate solution. The etching temperature and time can be attuned to prepare track-etched membrane with a desired pore diameter in the range of few hundred nanometers. Temperatures ranged between 55 °C and 65 °C were optimal to produce cylindrical pores. Temperatures higher than 85 °C induce conical-shaped track-etched pores while temperatures lower than 50 °C slow down the chemical attack. The addition of a phase-transfer agent enhances the chemical attack and allows the decrease of the etching temperature and/or time.

The hydrophilic modification of a polyvinylidene fluoride (PVDF) microfiltration membrane via pretreatment with argon plasma and direct surface-initiated atom transfer radical polymerization (ATRP) was studied. Both modified and unmodified PVDFmembranes were characterized by Fourier transform infrared spectroscopy (FTIR), water contact angle, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and pore size distribution measurements. FTIR and XPS spectra confirmed that sulfobetaine methacrylate (SBMA) had been grafted onto the membrane surface. The initial contact angle decreased from 87.0° to 29.8° and a water drop penetrated into the modified membrane completely in 8 s. The pore size distribution of the modified membrane exhibited a smaller mean value than that of the original membrane. The antifouling properties of the modified PVDFmembrane were evaluated by a filtration test using bovine serum albumin (BSA) solution. The results showed that the initial flux of the modified membrane increased from 2140.1 L/m2 h to 2812.7 L/m2 h and the equilibrium flux of BSA solution increased from 31 L/m2 h to 53 L/m2 h.

Poly(vinylidene fluorine) (PVDF) membranes were grafted by gamma-ray irradiation and were sulfonated by sodium sulfite to modify the surface of the membranes. The characteristics of the modified PVDFmembranes were evaluated by the data of Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscope (FE-SEM), the contact angle of the membrane surface and the water permeability. From the results of FT-IR, XPS and FE-SEM, it was shown that the modified membranes were successfully grafted by gamma-ray irradiation and were sulfonated. The content of oxygen and sulfur increased with the monomer concentration, while the content of fluorine sharply decreased. The pore size of the modified membranes decreased after gamma-ray irradiation. The contact angle and the water permeability showed that the hydrophilicity of the modified membranes played a role in determining the membrane performance. The feasibility study of the modified PVDFmembranes for using non-potable water reuse were carried out using a laboratory-scale microfiltration system. Grey wastewater was used as the influent in the filtration unit, and permeate quality satisfied non-potable water reuse guidelines in the Republic of Korea. PMID:25812106

We investigated the effect of different membrane polymeric materials on the relationship between membranepore size and development of membrane fouling in a membrane bioreactor (MBR). Membranes with different pore sizes were prepared using three different polymeric materials, cellulose acetate butyrate (CAB), polyvinyl butyral (PVB), and polyvinylidene fluoride (PVDF), and the development of membrane fouling in each membrane was evaluated by batch filtration tests using a mixed liquor suspension obtained from a laboratory-scale MBR. The results revealed that the optimal membranepore size to mitigate membrane fouling differed depending on membrane polymeric material. For PVDFmembranes, the degree of membrane fouling decreased as membranepore size increased. In contrast, CAB membranes with smaller pores had less fouling propensity than those with larger ones. Such difference can be attributed to the difference in major membrane foulants in each membrane; in PVDF, they were small colloids or dissolved organics in which proteins are abundant, and in CAB, microbial flocs. The results obtained in this study strongly suggested that optimum operating conditions of MBRs differ depending on the characteristics of the used membrane.

Press liquors are typical by-products of the citrus juice processing characterized by a high content of organic compounds and associated problems of environmental impact, which imply high treatment costs. However, these wastes contain a great number of health promoting substances, including fibers, carotenoids and phenolic compounds (mainly flavonoids), whose recovery against waste-destruction technologies is very attractive for new business opportunities. In this work, the clarification of orange press liquor by using microfiltration (MF) membranes is studied as a preliminary step to obtain a permeate stream enriched in antioxidant compounds which can be further processed to produce extracts of nutraceutical and/or pharmaceutical interest. MF poly(vinylidene fluoride) (PVDF) hollow fibers were prepared by the dry/wet spinning technique. A series of fibers was produced from the same polymeric dope, in order to investigate the effect of selected spinning parameters, i.e., bore fluid composition and flowrate, on their properties. The morphology of the produced fibers was analyzed by Scanning Electron Microscopy (SEM). Fibers were further characterized for their mechanical properties, porosity, bubble point, pore size distribution and pure water permeability (PWP). Some of the produced fibers exhibited high permeability (pure water permeability ~530 L/m2·h·bar), coupled to good mechanical resistance and pore size in the range of MF membranes. These fibers were selected and used for the clarification of press liquor from orange peel processing. In optimized operating conditions, the selected fibers produced steady-state fluxes of about 41 L/m2·h with rejections towards polyphenols and total antioxidant activity of 4.1% and 1.4%, respectively. PMID:26805899

Press liquors are typical by-products of the citrus juice processing characterized by a high content of organic compounds and associated problems of environmental impact, which imply high treatment costs. However, these wastes contain a great number of health promoting substances, including fibers, carotenoids and phenolic compounds (mainly flavonoids), whose recovery against waste-destruction technologies is very attractive for new business opportunities. In this work, the clarification of orange press liquor by using microfiltration (MF) membranes is studied as a preliminary step to obtain a permeate stream enriched in antioxidant compounds which can be further processed to produce extracts of nutraceutical and/or pharmaceutical interest. MF poly(vinylidene fluoride) (PVDF) hollow fibers were prepared by the dry/wet spinning technique. A series of fibers was produced from the same polymeric dope, in order to investigate the effect of selected spinning parameters, i.e., bore fluid composition and flowrate, on their properties. The morphology of the produced fibers was analyzed by Scanning Electron Microscopy (SEM). Fibers were further characterized for their mechanical properties, porosity, bubble point, pore size distribution and pure water permeability (PWP). Some of the produced fibers exhibited high permeability (pure water permeability ~530 L/m²·h·bar), coupled to good mechanical resistance and pore size in the range of MF membranes. These fibers were selected and used for the clarification of press liquor from orange peel processing. In optimized operating conditions, the selected fibers produced steady-state fluxes of about 41 L/m²·h with rejections towards polyphenols and total antioxidant activity of 4.1% and 1.4%, respectively. PMID:26805899

Current commercial polymer membranes have shown high performance and durability in water treatment, converting poor quality waters to higher quality suitable for drinking, agriculture and recycling. However, to extend the treatment into more challenging water sources containing abrasive particles, micro and ultrafiltration membranes with enhanced physical durability are highly desirable. This review summarises the current limits of the existing polymeric membranes to treat harsh water sources, followed by the development of nanocomposite poly(vinylidene fluoride) (PVDF) membranes for improved physical durability. Various types of nanofillers including nanoparticles, carbon nanotubes (CNT) and nanoclays were evaluated for their effect on flux, fouling resistance, mechanical strength and abrasion resistance on PVDFmembranes. The mechanisms of abrasive wear and how the more durable materials provide resistance was also explored. PMID:24957121

Efficiency of lithium-ion batteries largely relies on the performance of battery separator membrane as it controls the mobility and concentration of Li-ions between the anode and cathode electrodes. Recent advances in electrochemical strain microscopy (ESM) prompted the study of Li diffusion and transport at the nanoscale via electromechanical strain developed under an application of inhomogeneous electric field applied via the sharp ESM tip. In this work, we observed unexpectedly high electromechanical strain developed in polymer membranes based on porous poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) and, using it, could study a dynamics of electroosmotic flow of electrolyte inside the pores. We show that, independently of the separator membrane, electric field-induced deformation observed by ESM on wetted membrane surfaces can reach up to 10 nm under a moderate bias of 1 V (i.e., more than an order of magnitude higher than that in best piezoceramics). Such a high strain is explained by the electroosmotic flow in a porous media composed of PVDF. It is shown that the strain-based ESM method can be used to extract valuable information such as average pore size, porosity, elasticity of membrane in electrolyte solvent, and membrane-electrolyte affinity expressed in terms of zeta potential. Besides, such systems can, in principle, serve as actuators even in the absence of apparent piezoelectricity in amorphous PVDF. PMID:27142946

Transient circular pores can open in plasma membrane of cells due to mechanical stress, and failure to repair such pores lead to cell death. Similar pores in the form of defects also exist among smectic membranes, such as in myelin sheaths or mitochondrial membranes. The formation and growth of membrane defects are associated with diseases, for example multiple sclerosis. A deeper understanding of membranepore dynamics can provide a more refined picture of membrane integrity-related disease development, and possibly also treatment options and strategies. Pore dynamics is also of great importance regarding healthcare applications such as drug delivery, gene or as recently been implied, cancer therapy. The dynamics of pores significantly differ in stacks which are confined in 2D compared to those in cells or vesicles. In this short review, we will summarize the dynamics of different types of pores that can be observed in biological membranes, which include circular transient, fusion and hemi-fusion pores. We will dedicate a section to floral and fractal pores which were discovered a few years ago and have highly peculiar characteristics. Finally, we will discuss the repair mechanisms of large area pores in conjunction with the current cell membrane repair hypotheses.

Lipase is an enzyme having a lot of different industrial applications such as biodiesel production, biopolymer synthesis, enantiopure pharmaceutical productions, agrochemicals, etc. Its immobilized form on different substances is more conventional and useful than its free form. Supporting material was prepared using PVDF-co-HFP in laboratory conditions and attached 1,4-diaminobutane (DA) and epichlorohydrin (EPI) ligands to the membrane to immobilize lipase enzyme. The immobilization conditions such as enzyme amount, pH, the concentration of salt, thermal stability and activity were stabilized for our experimental setup. Then, biochemical characterizations were performed on immobilized lipase PVDF-co-HFP regarding optimal pH activity, temperature and thermal stability. Also, the desorption ratios of immobilized enzyme in two different pathway were investigated to confirm immobilization stability for 24 hours.

Temperature and pH responsive polymers (poly(N-isopropylacrylamide) (PNIPAAm), and polyacrylic acid, PAA) were synthesized in one common macrofiltration PVDFmembrane platform by pore-filling method. The microstructure and morphology of the PNIPAAm-PVDF, and PNIPAAm-FPAA-PVDFmembranes were studied by attenuated total reflectance Fourier transform infrared (ATR-FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The membranepore size was controlled by the swelling and shrinking of the PNIPAAm at the temperature around lower critical solution temperature (LCST). The composite membrane demonstrated a rapid and reversible swelling and deswelling change within a small temperature range. The controllable flux makes it possible to utilize this temperature responsive membrane as a valve to regulate filtration properties by temperature change. Dextran solution (Mw=2,000,000g/mol, 26 nm diameter) was used to evaluate the separation performance of the temperature responsive membranes. The ranges of dextran rejection are from 4% to 95% depending on the temperature, monomer amount and pressure. The full-scale membrane was also developed to confirm the feasibility of our bench-scale experimental results. The full-scale membrane also exhibited both temperature and pH responsivity. This system was also used for controlled nanoparticles synthesis and for dechlorination reaction. PMID:24944434

In this article, we report the preparation, characterization and microalgae recovery potential of a new family of fouling-resistant polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes embedded with hydrophilic and PEGylated polymeric particles. To optimize membrane performance for microalgae harvesting, we investigate the effects of three hydrophilic additives (Pluronic F-127, polyvinylpyrrolidone and polyethylene glycol) on the morphology, pore size, bulk composition, surface composition, wettability and surface charge, flux and fouling resistance of the mixed matrix PVDFmembranes with in situ PEGylated polyethyleneimine (PEI) particles. Our filtration experiments show that a mixed matrix PVDFmembrane with PEGylated PEI particles and Pluronic F-127 additive (PNSM-1) has an algae retention of 100% with a permeate flux of 96 L/m(2)/hr that is larger (by ∼50%) than that of a commercial and hydrophilic PVDF UF membrane with a molecular weight cut-off of 30 kDa using a suspension of Chlorella sp. KR-1 microalgae with 1.2-1.4 g/L of dry biomass. The algae and water flux recovery rates of our new PNSM-1 are equal to∼ 94% and 100%, respectively, following a simulated membrane wash with deionized water and two subsequent water and microalgae filtration cycles. PMID:25659965

Polyvinylidene fluoride (PVDF) membrane and PVDFmembrane with phenolphthalein polyethersulfone (PES-C) addition were prepared via thermally induced phase separation (TIPS) method by using diphenyl carbonate (DPC) and dimethyl acetamide (DMAc) as mixed diluents. The effects of coagulation temperature and pre-evaporation time on structure and properties of membranes were studied. The changes of sewage flux in MBR and the attenuation coefficient of sewage flux were investigated. The resistance distributions of PVDF and PVDF/PES-C membranes were compared by resistance analysis. Membrane composition and structure were characterized by ATR-FTIR, TGA, SEM and AFM. The foulant on membranes was analyzed by FTIR. The contact angle of PVDF/PES-C membrane was lower than that of PVDFmembrane. A thinner skin layer and a porous cellular support layer formed in PVDF/PES-C membrane and resulted in a higher porosity and pure water flux. The pure water flux and porosity of PVDF/PES-C membrane increased with rising coagulation temperature and decreased with extending pre-evaporation time. The flux attenuation coefficient, the cake layer resistance and internal fouling resistance of PVDF/PES-C membrane in MBR were smaller than those of PVDFmembrane in MBR. The FTIR spectrum of foulant on membrane indicated that the foulant on PVDF/PES-C membrane was mostly composed of protein and polysaccharide, while the foulant on pure PVDFmembrane included biopolymer clusters besides protein and polysaccharide.

Statistical experimental design was employed to optimize the preparation conditions of polyvinylidenefluoride (PVDF) membranes. Three variables considered were polymer concentration, dissolving temperature, and casting thickness, whereby the response variable was membrane-protein binding. The optimum preparation for the PVDFmembrane was a polymer concentration of 16.55 wt%, a dissolving temperature of 27.5°C, and a casting thickness of 450 µm. The statistical model exhibits a deviation between the predicted and actual responses of less than 5%. Further characterization of the formed PVDFmembrane showed that the morphology of the membrane was in line with the membrane-protein binding performance. PMID:27088961

Membrane surface and cross-sectional morphology created during membrane formation is one of the most essential factors determining membrane separation performance. However, the complicated interactions between added nanoparticles and additives influencing membrane morphology and performance during building membrane architectures had been generally neglected. In this study, asymmetric PVDF composite ultrafiltration (UF) membranes containing graphene oxides (GO) were prepared by using N-methyl pyrrolidone (NMP) as solvent and polyvinylpyrrodione (PVP) as the pore forming reagent. In the first time, the effects of mutual interactions between GO and PVP on membranes surface compositions, morphology and performance were investigated in detail. The variation in chemical properties of different membranes and hydrogen bonds in the membrane containing GO and PVP were confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR). Atomic force microscopy (AFM), scanning electron microscopy (SEM), and contact angle (CA) were utilized to clarify the synergetic effects of GO and PVP on morphologies and surface hydrophilicity of membranes. Besides, water flux, bovine serum albumin (BSA) rejection and attenuate coefficient were also determined to investigate filtration performance of various membranes. Compared with pure PVDFmembrane, the comprehensive performance of PVDF/GO/PVP membrane has been obviously improved. The surface hydrophilicity and anti-fouling performance were enhanced by the synergistic effects of incorporated GO and PVP. When the PVP content was 0.25 wt.% and the GO content was 0.5 wt.%, the optimized performance can be obtained due to the formation of hydrogen bonds between GO and PVP.

Magainin, found in the skin of Xenopus laevis, belongs to a broad class of antimicrobial peptides which kill bacteria by permeabilizing the cytoplasmic membrane but do not lyse eukaryotic cells. The 23-residue peptide has been shown to form an amphiphilic helix when associated with membranes. However, its molecular mechanism of action has been controversial. Oriented circular dichroism has detected helical magainin oriented perpendicular to the plane of the membrane at high peptide concentrations, but Raman, fluorescence, differential scanning calorimetry, and NMR all indicate that the peptide is associated with the head groups of the lipid bilayer. Here we show that neutron in-plane scattering detects pores formed by magainin 2 in membranes only when a substantial fraction of the peptide is oriented perpendicular to the membrane. The pores are almost twice as large as the alamethicin pores. On the basis of the in-plane scattering data, we propose a toroidal (or wormhole) model, which differs from the barrel-stave model of alamethicin in that the lipid bends back on itself like the inside of a torus. The bending requires a lateral expansion in the head group region of the bilayer. Magainin monomers play the role of fillers in the expansion region thereby stabilizing the pore. This molecular configuration is consistent with all published magainin data. PMID:8901513

Herein we report a new ammoniation-based chemical modification strategy for synthesis of continuous and uniform metal-organic framework (MOF)/polyvinylidene fluoride (PVDF) membranes with attractive performance. Ammoniation can promote the support PVDFmembrane to produce amino groups, form a nanoparticle structure, and be well cross-linked; therefore, the high-density heterogeneous nucleation sites for MOFs growth were provided and the thermal stability and chemical resistance of composite membranes can be greatly improved. The high-quality layers of representative Cu-BTC and ZIF-8 were synthesized on the chemically modified PVDFmembranes. By ammoniation, ZIF-7 can even be grown under harsh synthetic conditions such as in DMF precursor solutions at 403 K. The fabricated MOF/PVDF composite membranes with excellent hollow fiber structures and enhanced structural stability exhibited high H2 permselectivities for H2 /CO2 and H2 /N2 . PMID:25810142

A membrane consisting of a blend of sulfonated poly(ether ether ketone) (SPEEK), poly(vinylidene fluoride) (PVDF), and poly(ether sulfone) (PES) has been fabricated and used as an ion exchange membrane for application in vanadium redox flow batteries (VRBs). The vanadium ion permeability of the SPEEK/PVDF/PES membrane was one order of magnitude lower than that of Nafion 117 membrane. The low-cost composite membrane exhibited better performance than Nafion 117 membrane at the same operating condition. A VRB single cell with SPEEK/PVDF/PES membrane showed significantly lower capacity loss, higher coulombic efficiency (>95%), and higher energy efficiency (>82%) compared with Nafion 117 membrane. In the self-discharge test, the duration of the cell with the SPEEK/PVDF/PES membrane was nearly two times longer than that with Nafion 117 membrane. Considering these good properties and its low cost, SPEEK/PVDF/PES membrane is expected to have excellent commercial prospects as an ion exchange membrane for VRB systems.

Polyvinylidene fluoride (PVDF) based polymer electrolytes have a high dielectric constant, which can assist in greater ionization of lithium salts. The main advantages of PVDF are its durability in long battery operation and its ability to be a good ion conductor. However, the limitation of this polymer is its crystalline molecular structure. Dispersing nano-particles in the polymer matrix may improve the characteristics of the PVDF polymer. This paper aims to investigate the impact of nano-clay addition on the characteristics of PVDF polymer to be used as a polymer electrolyte membrane. In addition, the effect of poly(vinyl pyrrolidone) (PVP) is also investigated. The membrane was prepared by phase separation method whereas the polymer electrolyte membranes was prepared by immersing into 1 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate/dimethyl carbonate (EC/DMC) electrolytes for 1 h. The membranes were characterized by scanning electron microscope (SEM), porosity and electrolyte uptake and performance in battery cell. The results showed that both nano-clay and PVP have significant impacts on the improvement of PVDFmembranes to be used as polymer electrolyte.

Covalent bonding of graphene oxide quantum dots (GOQDs) onto amino modified polyvinylidene fluoride (PVDF) membrane has generated a new type of nano-carbon functionalized membrane with significantly enhanced antibacterial and antibiofouling properties. A continuous filtration test using E. coli containing feedwater shows that the relative flux drop over GOQDs modified PVDF is 23%, which is significantly lower than those over pristine PVDF (86%) and GO-sheet modified PVDF (62%) after 10 h of filtration. The presence of GOQD coating layer effectively inactivates E. coli and S. aureus cells, and prevents the biofilm formation on the membrane surface, producing excellent antimicrobial activity and potentially antibiofouling capability, more superior than those of previously reported two-dimensional GO sheets and one-dimensional CNTs modified membranes. The distinctive antimicrobial and antibiofouling performances could be attributed to the unique structure and uniform dispersion of GOQDs, enabling the exposure of a larger fraction of active edges and facilitating the formation of oxidation stress. Furthermore, GOQDs modified membrane possesses satisfying long-term stability and durability due to the strong covalent interaction between PVDF and GOQDs. This study opens up a new synthetic avenue in the fabrication of efficient surface-functionalized polymer membranes for potential waste water treatment and biomolecules separation. PMID:26832603

Covalent bonding of graphene oxide quantum dots (GOQDs) onto amino modified polyvinylidene fluoride (PVDF) membrane has generated a new type of nano-carbon functionalized membrane with significantly enhanced antibacterial and antibiofouling properties. A continuous filtration test using E. coli containing feedwater shows that the relative flux drop over GOQDs modified PVDF is 23%, which is significantly lower than those over pristine PVDF (86%) and GO-sheet modified PVDF (62%) after 10 h of filtration. The presence of GOQD coating layer effectively inactivates E. coli and S. aureus cells, and prevents the biofilm formation on the membrane surface, producing excellent antimicrobial activity and potentially antibiofouling capability, more superior than those of previously reported two-dimensional GO sheets and one-dimensional CNTs modified membranes. The distinctive antimicrobial and antibiofouling performances could be attributed to the unique structure and uniform dispersion of GOQDs, enabling the exposure of a larger fraction of active edges and facilitating the formation of oxidation stress. Furthermore, GOQDs modified membrane possesses satisfying long-term stability and durability due to the strong covalent interaction between PVDF and GOQDs. This study opens up a new synthetic avenue in the fabrication of efficient surface-functionalized polymer membranes for potential waste water treatment and biomolecules separation.

Covalent bonding of graphene oxide quantum dots (GOQDs) onto amino modified polyvinylidene fluoride (PVDF) membrane has generated a new type of nano-carbon functionalized membrane with significantly enhanced antibacterial and antibiofouling properties. A continuous filtration test using E. coli containing feedwater shows that the relative flux drop over GOQDs modified PVDF is 23%, which is significantly lower than those over pristine PVDF (86%) and GO-sheet modified PVDF (62%) after 10 h of filtration. The presence of GOQD coating layer effectively inactivates E. coli and S. aureus cells, and prevents the biofilm formation on the membrane surface, producing excellent antimicrobial activity and potentially antibiofouling capability, more superior than those of previously reported two-dimensional GO sheets and one-dimensional CNTs modified membranes. The distinctive antimicrobial and antibiofouling performances could be attributed to the unique structure and uniform dispersion of GOQDs, enabling the exposure of a larger fraction of active edges and facilitating the formation of oxidation stress. Furthermore, GOQDs modified membrane possesses satisfying long-term stability and durability due to the strong covalent interaction between PVDF and GOQDs. This study opens up a new synthetic avenue in the fabrication of efficient surface-functionalized polymer membranes for potential waste water treatment and biomolecules separation. PMID:26832603

A highly hydrophilic PVDFmembrane was fabricated through chemically binding TiO2 nanoparticles and a poly(vinyl alcohol) (PVA) layer onto a membrane surface simultaneously. The chemical composition of the modified membrane surface was determined by X-ray photoelectron spectroscopy, and the binding performance of TiO2 nanoparticles and the PVA layer was investigated by a rinsing test. The results indicated that the TiO2 nanoparticles were uniformly and strongly tailored onto the membrane surface, while the PVA layer was firmly attached onto the surface of TiO2 nanoparticles and the membrane by adsorption-cross-linking. The possible mechanisms during the modification process and filtration performance, i.e., water permeability and bovine serum albumin (BSA) rejection, were investigated as well. Furthermore, antifouling property was discussed through multicycles of BSA solution filtration tests, where the flux recovery ratio was significantly increased from 20.0% for pristine PVDFmembrane to 80.5% for PVDF/TiO2/PVA-modified membrane. This remarkable promotion is mainly ascribed to the improvement of surface hydrophilicity, where the water contact angle of the membrane surface was decreased from 84° for pristine membrane to 24° for PVDF/TiO2/PVA membrane. This study presents a novel and varied strategy for immobilization of nanoparticles and PVA layer on substrate surface, which could be easily adapted for a variety of materials for surface modification. PMID:25806418

Based on a two-step polymerization method, two sulfobetaine-based zwitterionic monomers, including 3-(methacryloylamino) propyl-dimethyl-(3-sulfopropyl) ammonium hydroxide (MPDSAH) and 2-(methacryloyloxyethyl) ethyl-dimethyl-(3-sulfopropyl) ammonium (MEDSA), were successfully grafted from poly(vinylidene fluoride) (PVDF) hollow fiber membrane surfaces in the presence of N,N'-methylene bisacrylamide (MBAA) as a cross-linking agent. The mechanical properties of the PVDFmembrane were improved by the zwitterionic surface layers. The surface hydrophilicity of PVDFmembranes was significantly enhanced and the polyMPDSAH-g-PVDFmembrane showed a higher hydrophilicity due to the higher grafting amount. Compared to the polyMEDSA-g-PVDFmembrane, the polyMPDSAH-g-PVDFmembrane showed excellent significantly better anti-protein-fouling performance with a flux recovery ratio (RFR) higher than 90% during the cyclic filtration of a bovine serum albumin (BSA) solution. The polyMPDSAH-g-PVDFmembrane showed an obvious electrolyte-responsive behavior and its protein-fouling-resistance performance was improved further during the filtration of the protein solution with 100 mmol/L of NaCl. After cleaned with a membrane cleaning solution for 16 days, the grafted MPDSAH layer on the PVDFmembrane could be maintain without any chang; however, the polyMEDSA-g-PVDFmembrane lost the grafted MEDSA layer after this treatment. Therefore, the amide group of sulfobetaine, which contributed significantly to the higher hydrophilicity and stability, was shown to be imperative in modifying the PVDFmembrane for a stable anti-protein-fouling performance via the two-step polymerization method. PMID:24957171

Based on a two-step polymerization method, two sulfobetaine-based zwitterionic monomers, including 3-(methacryloylamino) propyl-dimethyl-(3-sulfopropyl) ammonium hydroxide (MPDSAH) and 2-(methacryloyloxyethyl) ethyl-dimethyl-(3-sulfopropyl) ammonium (MEDSA), were successfully grafted from poly(vinylidene fluoride) (PVDF) hollow fiber membrane surfaces in the presence of N,N′-methylene bisacrylamide (MBAA) as a cross-linking agent. The mechanical properties of the PVDFmembrane were improved by the zwitterionic surface layers. The surface hydrophilicity of PVDFmembranes was significantly enhanced and the polyMPDSAH-g-PVDFmembrane showed a higher hydrophilicity due to the higher grafting amount. Compared to the polyMEDSA-g-PVDFmembrane, the polyMPDSAH-g-PVDFmembrane showed excellent significantly better anti-protein-fouling performance with a flux recovery ratio (RFR) higher than 90% during the cyclic filtration of a bovine serum albumin (BSA) solution. The polyMPDSAH-g-PVDFmembrane showed an obvious electrolyte-responsive behavior and its protein-fouling-resistance performance was improved further during the filtration of the protein solution with 100 mmol/L of NaCl. After cleaned with a membrane cleaning solution for 16 days, the grafted MPDSAH layer on the PVDFmembrane could be maintain without any chang; however, the polyMEDSA-g-PVDFmembrane lost the grafted MEDSA layer after this treatment. Therefore, the amide group of sulfobetaine, which contributed significantly to the higher hydrophilicity and stability, was shown to be imperative in modifying the PVDFmembrane for a stable anti-protein-fouling performance via the two-step polymerization method. PMID:24957171

Polyvinylidene fluoride (PVDF) has drawn much attention as a predominant ultrafiltration (UF) membrane material due to its outstanding mechanical and physicochemical properties. However, current applications suffer from the low fouling resistance of the PVDFmembrane due to the intrinsic hydrophobic property of the membrane. The present study demonstrates a novel approach for the fabrication of a highly hydrophilic PVDF UF membrane via postfabrication tethering of superhydrophilic silica nanoparticles (NPs) to the membrane surface. The pristine PVDFmembrane was grafted with poly(methacrylic acid) (PMAA) by plasma induced graft copolymerization, providing sufficient carboxyl groups as anchor sites for the binding of silica NPs, which were surface-tailored with amine-terminated cationic ligands. The NP binding was achieved through a remarkably simple and effective dip-coating technique in the presence or absence of the N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) cross-linking process. The properties of the membrane prepared from the modification without EDC/NHS cross-linking were comparable to those for the membrane prepared with the EDC/NHS cross-linking. Both modifications almost doubled the surface energy of the functionalized membranes, which significantly improved the wettability of the membrane and converted the membrane surface from hydrophobic to highly hydrophilic. The irreversibly bound layer of superhydrophilic silica NPs endowed the membranes with strong antifouling performance as demonstrated by three sequential fouling filtration runs using bovine serum albumin (BSA) as a model organic foulant. The results suggest promising applications of the postfabrication surface modification technique in various membrane separation areas. PMID:23796125

Microporous poly(vinylidene fluoride) (PVDF) membranes with dense or porous surface were prepared by immersion precipitation of PVDF/TEP solutions in coagulation baths containing different amounts of water. Onto the membrane surface, poly(glycidyl methacrylate) (PGMA) was grafted by plasma-induced free radical polymerization. Then, L-lysine was covalently bonded to the as-grafted PGMA through ring-opening reactions between epoxide and amine to form amino alcohol. The highest attainable graft density of PGMA on a PVDFmembrane was 0.293 mg/cm2. This was obtained when the reaction was carried out on a porous surface under an optimized reaction condition. For immobilization of L-lysine, the yield was found to depend on the reaction temperature and L-lysine concentration. The maximal yield was 0.226 mg/cm2, a value considerably higher than reported in the literature using other immobilization methods. Furthermore, neurons were cultured on L-lysine-immobilized PVDFmembranes. The results indicated that these membrane surfaces were suited to the growth of neurons, with a MTT value higher than that of the standard culture dish. PMID:19323885

On the basis of the excellent fouling resistance of zwitterionic materials, the super antifouling polyvinylidene fluoride (PVDF) membrane was efficiently prepared though one-step sulfonation of PVDF and polyaniline blend membrane in situ. The self-doped sulfonated polyaniline (SPANI) was generated as a novel zwitterionic polymer to improve the antifouling property of PVDF ultrafiltration membrane used in sewage treatment. Surface attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, surface zeta potential, and water contact angle demonstrated the successful fabrication of zwitterionic interface by convenient sulfonation modification. The static adsorption fouling test showed the quantified adsorption mass of bovine serum albumin (BSA) pollutant on the PVDF/SPANI membrane surface decreases to 3(±2) μg/cm(2), and the water flux recovery ratio (FRR) values were no less than 95% for the three model pollutants of BSA, sodium alginate (SA), and humic acid (HA), which were corresponding hydrophobic, hydrophilic, and natural pollutants in sewage, respectively. This Research Article demonstrated the antifouling advantages of zwitterionic SPANI and aimed to provide a simple method for the large scale preparation of zwitterionic antifouling ultrafiltration membranes. PMID:26218230

Epoxidised Natural Rubber (ENR) / Poly (Vinylidene Fluoride) (PVDF) (ENR/PVDF) (60:40 wt%) thin film composite membrane was prepared by using solution casting technique. The focuses of this paper are to prepare ENR/PVDFmembrane with ratio of ENR to PVDF 60:40 wt%, and to study the effectiveness of treating Palm Oil Mill Effluent (POME) using the membrane. The prepared membrane was analyzed using optical microscope and the treatment of POME was investigated using dead-end stirred cell. Treated and untreated POME was analyzed to test the percentage of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) removal. Optical microscope micrographs showed that the surface of the membrane was slightly uneven. The rate of flux which passed through the membrane was 0.60 L/hm2. Both BOD and COD decreased by 23.6 % and 49.32 % respectively, after single treatment. This showed that the membrane can be used for POME treatment. The value of BOD and COD removal can be increased by recycling the treated POME for more than two cycles, which will be further studied by authors.

Pneumolysin is a member of the cholesterol-dependent cytolysin (CDC) family of pore-forming proteins that are produced as water-soluble monomers or dimers, bind to target membranes and oligomerize into large ring-shaped assemblies comprising approximately 40 subunits and approximately 30 nm across. This pre-pore assembly then refolds to punch a large hole in the lipid bilayer. However, in addition to forming large pores, pneumolysin and other CDCs form smaller lesions characterized by low electrical conductance. Owing to the observation of arc-like (rather than full-ring) oligomers by electron microscopy, it has been hypothesized that smaller oligomers explain smaller functional pores. To investigate whether this is the case, we performed cryo-electron tomography of pneumolysin oligomers on model lipid membranes. We then used sub-tomogram classification and averaging to determine representative membrane-bound low-resolution structures and identified pre-pores versus pores by the presence of membrane within the oligomeric curve. We found pre-pore and pore forms of both complete (ring) and incomplete (arc) oligomers and conclude that arc-shaped oligomeric assemblies of pneumolysin can form pores. As the CDCs are evolutionarily related to the membrane attack complex/perforin family of proteins, which also form variably sized pores, our findings are of relevance to that class of proteins as well. PMID:24759615

A novel hydrophilic nanocomposite additive (PVP-g-MMT), coupling of hydrophilic modifier, self-dispersant, and pore-forming agent (porogen), was synthesized by the surface modification of montmorillonite (MMT) with N-vinylpyrrolidone (NVP) via "grafting from" polymerization in the presence of H(2)O(2)-NH(3)·H(2)O as the initiator, and then the nanocomposite membrane of poly(vinylidene fluoride) (PVDF) and PVP-g-MMT was fabricated by wet phase inversion onto clean glass plates. The existence and dispersion of PVP-g-MMT had a great role on structures, morphologies, surface composition, and chemistry of the as-prepared nanocomposite membranes confirmed by varieties of spectroscopic and microscopic characterization techniques, all of which were the correlated functions of PVP-g-MMT content in casting solution. By using the dead-end filtration of protein aqueous solution, the performance of the membrane was evaluated. It was seen that all of the nanocomposite membranes showed obvious improvement of water flux and proper BSA rejection ratio, compared to the control PVDFmembrane. Meanwhile, dynamic BSA fouling resistance and flux recovery properties were also greatly enhanced due to the changes of surface hydrophilicity and morphologies. All the experimental results indicated that the as-prepared PVDF nanocomposite membranes showed better separation performances than the control PVDFmembrane. Hopefully, the demonstrated method of hydrophilic nanocomposite additive synthesis would be applied for commonly hydroxyl group-containing inorganic nanoparticles, which was favorable to fabricate hydrophilic nanoparticle-enhanced polymer membranes for water treatment. PMID:22376185

Dual layer polyvinylidene fluoride (PVDF), antibacterial, hollow fiber, ultra-filtration composite membranes with antibacterial particles (silver (Ag) nano-particles loaded zeolite (Z-Ag)) in the outer layer were prepared with high water flux and desired pore sizes. The amounts of Ag(+) released from the composite membranes, freshly made and stored in water and salt solution, were measured. The result indicated that dual layer PVDF antibacterial hollow fiber containing Z-Ag (M-1-Ag) still possessed the ability of continuous release of Ag(+) even after exposure to water with high ionic content, showing a longer term resistance to bacterial adhesion and antibacterial activity than membrane doped with Z-Ag(+) (M-1). Results from an anti-adhesion and bacteria killing test with Escherichia coli supported that the antibacterial efficiency of dual hollow fiber PVDFmembranes with Z-Ag was much higher than those with Z-Ag(+) after long time storage in water or exposure to phosphate buffered saline (PBS) solution. This novel hollow fiber membrane may find applications in constructing sea water pretreatment devices with long term antifouling capability for the desalination processes. PMID:27148717

Novel polyvinylidene fluoride (PVDF) ultrafiltration membranes were prepared by blending with different contents of titanium dioxide-halloysite nanotubes (TiO2-HNTs) composites into the PVDF matrix. The effects of TiO2-HNTs content on the membrane performances, such as hydrophilicity, rejection ratio and antifouling properties were investigated in detail. X-ray diffraction (XRD), thermo-gravimetric analyzer (TGA) and scanning electron microscope (SEM) analyses showed that TiO2 was loaded on the surface of HNTs successfully and homogeneously by sol-gel method. The morphologies and microstructure of the membranes were characterized by SEM and atomic force microscopy (AFM). The contact angle (CA) tests indicated that the hydrophilicity of membranes was significantly increased with the addition of TiO2-HNTs. The pure water flux of 3%TiO2-HNTs/PVDF was increased by 264.8% and 35.6%, respectively, compared with pure PVDFmembrane and 3%TiO2/PVDFmembrane, although the rejection of bovine serum albumin (BSA) was slightly decreased. More importantly, TiO2-HNTs/PVDFmembrane exhibited an excellent anti-fouling performance, which was attributed to the hydrophobic contaminants being resisted by hydrophilic nanoparticles. It can be expected that this work may provide some references to solve the dispersion of nanoparticle in the membrane and improve the anti-fouling performance of membrane in the field of wastewater treatment.

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane, with its excellent chemical and mechanical properties, has good potential for broad applications. However, due to its hydrophobic nature, microbial colonization is commonly encountered. In this work, electrospun PVDF-HFP fibrous membranes were surface modified by poly(4-vinyl- N-alkylpyridinium bromide) to achieve antibacterial activities. The membranes were first subjected to plasma pretreatment followed by UV-induced surface graft copolymerization of 4-vinylpyridine (4VP) and quaternization of the grafted pyridine groups with hexylbromide. The chemical composition of the surface modified PVDF-HFP electrospun membranes was studied by X-ray photoelectron spectroscopy (XPS). The morphology and mechanical properties of pristine and surface modified PVDF-HFP fibrous membranes were characterized by scanning electron microscopy (SEM) and tensile test, respectively. The antibacterial activities of the modified electrospun PVDF-HFP fibrous membranes were assessed against Gram-positive Staphylococcus aureus ( S. aureus) and Gram-negative Escherichia coli ( E. coli). The results showed that the PVDF-HFP fibrous membranes modified with quaternized pyridinium groups are highly effective against both bacteria with killing efficiency as high as 99.9999%.

Poly(vinylidene fluoride) (PVDF) was modified by chemical treatments in order to create active double bonds to obtain covalent grafting of poly(acrylic acid) (PAA) on membrane. The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectrum confirms the formation of conjugated C=C double bonds with surface dehydrofluorination. The membrane morphology was studied by scanning electron microscopy (SEM). The surface composition was characterized by X-ray photoelectron spectroscopy (XPS). The thermal stability of the dehydrofluorinated membrane (Def-PVDF) and functionalized membranes were investigated by differential scanning calorimetry (DSC) analysis. The influence of covalently attached PAA on Def-PVDFmembrane has been investigated to determine its effect on the transport of water and charged solute. Variations in the solution pH show an effect on both permeability and solute retention in a reversible fashion. Metal nanoparticles were also immobilized in the membrane for the degradation of toxic chlorinated organics from water. In addition, PVDFmembranes with an asymmetric and sponge-like morphology were developed by immersion-precipitation phase-inversion methods in both lab-scale and large-scale. The new type of spongy PVDFmembrane shows high surface area with higher yield of PAA functionalization. The ion-capacity with Ca2+ ions was also investigated. PMID:26074669

In this study, the poly(vinylidene fluoride) (PVDF) membrane was prepared via immersion precipitation technique and modified by UV photo-grafting of hydrophilic monomers on the top membrane surface. Acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) as acrylic monomers and 2,4-phenylenediamine (PDA) and ethylene diamine (EDA) as amino monomers were used at different concentrations to modify the membrane and improve the hydrophilicity with less fouling tendency. Moreover the presence of benzophenon as photo-initiator for grafting the hydrophilic monomers onto PVDFmembrane surface was elucidated. The virgin and modified PVDFmembranes were characterized by contact angle, ATR-FTIR, SEM and cross-flow filtration. The contact angle measurements demonstrated that the hydrophilicities of the membranes were significantly enhanced by UV photo-grafting of hydrophilic monomers onto the membrane surface. The ATR-FTIR confirmed the occurrence of modification on PVDFmembrane by UV photo-grafting. The pure water flux of membranes was declined by UV photo-grafting but the milk water permeation and protein rejection were slightly improved. Moreover the antifouling properties and flux recovery of PVDFmembrane were improved by UV photo-grafting of hydrophilic monomers.

Simultaneous gamma irradiation was used effectively for grafting of glycidyl methacrylic acid and styrene onto Poly vinyldine fluoride (PVDF). Membranes were characterized by thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM). The properties of the obtained membranes were evaluated in terms of proton conductivity, methanol permeability and positron annihilation lifetime (PALS) parameters. The high probability of Positronium formation enables the application of PALS to the study of free volume. Good property values approved the applicability of the membrane from the cost benefit point of view.

This paper describes a facile and novel approach for the surface glycosylation of poly(vinylidene difluoride) (PVDF) microporous membrane. A glycopolymer poly(D-gluconamidoethyl methacrylate) (PGAMA) was tethered onto the membrane surface via activators generated by electron transfer atom transfer radical polymerization (AGET ATRP) directly initiated from the PVDF surface. Chemical changes of membrane surface were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was revealed that PGAMA was successfully grafted onto the membrane surface and its grafting density can be modulated in a wide range up to 2.4 μmol/cm2. The effects of glycosylation on membrane morphology, flux and surface hydrophilicity were investigated. Field emission scanning electron microscopy (FESEM) results indicated shrinkage of the surface pore diameters and the growth of the glycopolymer layer on the membrane surface. The static water contact angle (WCA) of the membrane surface decreased from 110° to 30.4° with the increase of grafting density, indicating that the PGAMA grafts dramatically improved the surface hydrophilicity. The protein adsorption and platelets adhesion experiments indicated that the grafted PGAMA could effectively improve the membrane antifouling property and biocompatibility.

In the present study, nano-sized TiO(2)/Al(2)O(3) modified polyvinylidene fluoride (PVDF) membranes (MM) were fabricated and then utilized for oil/water emulsion separation. The results showed that, compared with PVDFmembrane (OM), the contact angle of MM decreased and hydrophilicity increased. The ultrafiltration (UF) of oil in water emulsions with transmembrane pressure (TMP) increasing results in a sharp fall in relative flux with time. The cake filtration models did not always predict the performance over the complete range of filtration times very well. In the initial 30 min, all the four cake models can simulate this UF process to a certain extent, and the suitability was: cake filtration > intermediate pore blocking > standard pore blocking > complete pore blocking models. However, they were no longer adapted well with UF time extent to 60 min, but only cake filtration (R(2) = 0.9535) maintained a high adaptability. Surface and cross-sectional morphology of the membrane was investigated by SEM to make an advanced certificate of this UF mechanism. PMID:23202550

Structures that can be interpreted as cytoplasm droplets leaking through the membrane are experimentally detected on the membranes of adipocytes using optical digital microscopy. The effect of an aqueous alcohol solution of brilliant green on the amount and sizes of structures is studied. It is demonstrated that the optical irradiation of the adipocytes that are sensitized with the aid of the brilliant green leads to an increase in the amount of structures (pores) after the irradiation. The experimental results confirm the existence of an earlier-proposed effect of photochemical action on the sensitized cells of adipose tissue that involves additional formation of pores in the membrane of the sensitized cell under selective optical irradiation. The proposed method for the detection of micropores in the membrane of adipose tissue based on the detection of the cytoplasm droplets leaking from the cell can be considered as a method for the optical detection of nanosized pores.

Novel PVDF/TiO2 hybrid membranes were prepared by phase inversion process from a PVDF/DMAc/PVP/tetrabutyltitanate/water system. The membrane characteristics such as morphology, thermal properties, porosity, water contact angle, tensile strength and separability were investigated by a series of analytical methods including atomic force microscope (AFM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and zeta potential measurements. The performances and surface properties of hybrid and PVDFmembranes were tested by the removal of bovine serum albumin (BSA) from aqueous solution, evaluated by using two dyes with different charge (congo red and methylene blue). Based on the experimental results, TiO2 nanoparticles of a quantum size (~8 nm or less) in anatase crystal structure were obtained from the controlled hydrolysis of tetrabutyltitanate. Besides, TiO2 sol was introduced into polymer molecule for the hybrid membrane with less than 12 vol % TiO2 sol to PVDF and contributed to a smooth surface and more apertures due to both the interaction and compatibility between polymer and TiO2 sol, to which the improvement in hydrophilicity, thermal stability, mechanical strength and antifouling ability is attributed. The observed rejections were optimized for PVDF/TiO2 hybrid membrane with respect to PVDFmembrane. In particular, the pure water permeation flux was increased from126.6 to166.7 L/m2•h for hybrid membrane with a relative flux of 80 % compared to 50 % of relative flux observed for PVDFmembrane.

Frost, the solid deposition of water vapor from humid air, forms on the surface of a solid substrate when its temperature drops below the freezing point of water. In this study, we demonstrate how this natural phenomenon can be applied to develop novel nanoporous materials. The solvent annealing of polyvinylidene fluoride (PVDF) infiltrated into nanopores induced template-directed dewetting thus preparing nanoembossing films. Then, water nanodroplets formed on the cold polymer nanopatterned surfaces following the embossing patterns, similar to dew formation on the ground. Subsequently, the nanodroplets were frozen and then removed by freeze-drying. This nano-frost array technique produced nanoporous PVDFmembranes with an average thickness of 250 (+/-48) nm. It was revealed that the nanopatterned surface formed by solvent annealing played an important role in achieving a nano-frost array with an adjustable size. Additionally, the freezing process led to significant changes of the PVDF crystallinity and polymorphism. Our results prove that the nano-frost array technique can be broadly used to design ordered nanoporous structures and provide new prospects in nanomaterial fields.Frost, the solid deposition of water vapor from humid air, forms on the surface of a solid substrate when its temperature drops below the freezing point of water. In this study, we demonstrate how this natural phenomenon can be applied to develop novel nanoporous materials. The solvent annealing of polyvinylidene fluoride (PVDF) infiltrated into nanopores induced template-directed dewetting thus preparing nanoembossing films. Then, water nanodroplets formed on the cold polymer nanopatterned surfaces following the embossing patterns, similar to dew formation on the ground. Subsequently, the nanodroplets were frozen and then removed by freeze-drying. This nano-frost array technique produced nanoporous PVDFmembranes with an average thickness of 250 (+/-48) nm. It was revealed that the

Advances in industrial ecology, desalination, and resource recovery have established that industrial wastewater, seawater, and brines are important and largely untapped sources of critical metals and elements. A Grand Challenge in metal recovery from industrial wastewater is to design and synthesize high capacity, recyclable and robust chelating ligands with tunable metal ion selectivity that can be efficiently processed into low-energy separation materials and modules. In our efforts to develop high capacity chelating membranes for metal recovery from impaired water, we report a one-pot method for the preparation of a new family of mixed matrix polyvinylidene fluoride (PVDF) membranes with in situ synthesized poly(amidoamine) [PAMAM] particles. The key feature of our new membrane preparation method is the in situ synthesis of PAMAM dendrimer-like particles in the dope solutions prior to membrane casting using low-generation dendrimers (G0 and G1-NH2) with terminal primary amine groups as precursors and epichlorohydrin (ECH) as cross-linker. By using a combined thermally induced phase separation (TIPS) and nonsolvent induced phase separation (NIPS) casting process, we successfully prepared a new family of asymmetric PVDF ultrafiltration membranes with (i) neutral and hydrophilic surface layers of average pore diameters of 22-45 nm, (ii) high loadings (∼48 wt %) of dendrimer-like PAMAM particles with average diameters of ∼1.3-2.4 μm, and (iii) matrices with sponge-like microstructures characteristics of membranes with strong mechanical integrity. Preliminary experiments show that these new mixed matrix PVDFmembranes can serve as high capacity sorbents for Cu(II) recovery from aqueous solutions by ultrafiltration. PMID:26222014

A novel zwitterionic surface of PVDFmembrane with significantly improved antifouling properties was prepared though pressure-assisted layer by layer self-assembly method based on the electrostatic interactions of chitosan (CS), sodium alginate (SA) and polyfunctional lysine. For the modified C-S-C-S-L membrane, the contact angle decreased to 35°, the bovine serum albumin (BSA) adsorption mass of static fouling on the membrane surface decreased to 10μg/cm(2), and the secondary water flux recovery rate (FRR) of dynamic fouling of BSA and humic acid (HA) pollutants increased to 98% and 99%, respectively, exhibiting excellent antifouling performance. The results demonstrated that using charged bio-macromolecules and amino acids to build zwitterionic surface was effective and convenient to change the interface properties of the separation membrane through the pressure-assisted self-assembly modification method, and provided a new way for the industrial scale hydrophilic modification of hydrophobic porous membrane materials. PMID:26944663

Frost, the solid deposition of water vapor from humid air, forms on the surface of a solid substrate when its temperature drops below the freezing point of water. In this study, we demonstrate how this natural phenomenon can be applied to develop novel nanoporous materials. The solvent annealing of polyvinylidene fluoride (PVDF) infiltrated into nanopores induced template-directed dewetting thus preparing nanoembossing films. Then, water nanodroplets formed on the cold polymer nanopatterned surfaces following the embossing patterns, similar to dew formation on the ground. Subsequently, the nanodroplets were frozen and then removed by freeze-drying. This nano-frost array technique produced nanoporous PVDFmembranes with an average thickness of 250 (± 48) nm. It was revealed that the nanopatterned surface formed by solvent annealing played an important role in achieving a nano-frost array with an adjustable size. Additionally, the freezing process led to significant changes of the PVDF crystallinity and polymorphism. Our results prove that the nano-frost array technique can be broadly used to design ordered nanoporous structures and provide new prospects in nanomaterial fields. PMID:24865989

Characterization of membrane proteins remains an analytical challenge because of difficulties associated with tedious isolation and purification. This study presents the utility of the polyvinylidene difluoride (PVDF) membrane for direct sub-proteome profiling and membrane protein characterization by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The hydrophobic adsorption of protein, particularly membrane proteins, on the PVDF surface enables efficient on-PVDF washing to remove high concentrations of detergents and salts, such as up to 5% sodium dodecyl sulfate (SDS). The enhanced spectrum quality for MALDI detection is particularly notable for high molecular weight proteins. By using on-PVDF washing prior to MALDI detection, we obtained protein profiles of the detergent-containing and detergent-insoluble membrane fractions from Methylococcus capsulatus (Bath). Similar improvements of signal-to-noise ratios were shown on the MALDI spectra for proteins electroblotted from SDS-polyacrylamide gel electrophoresis (SDS-PAGE) onto the PVDFmembrane. We have applied this strategy to obtain intact molecular weights of the particulate methane monooxygenase (pMMO) composed of three intrinsic membrane-bound proteins, PmoA, PmoB, and PmoC. Together with peptide sequencing by tandem mass spectrometry, post-translational modifications including N-terminal acetylation of PmoA and PmoC and alternative C-terminal truncation of PmoB were identified. The above results show that PVDF-aided MALDI-MS can be an effective approach for profiling and characterization of membrane proteins. PMID:17723354

In this paper, we propose a ferro-actuator using a porous polyvinylidene difluoride (PVDF) membrane. In detail, we fabricated the silica-embedded PVDFmembrane using a sol-gel process with PVDF solution and tetraethyl orthosilicate (TEOS) solution, where the size of the silica was determined by the ratio of the PVDF and TEOS solutions. Using hydrofluoric acid (HF) etching, the silica were removed from the silica-embedded PVDFmembrane, and porous PVDFmembranes with different porosities were obtained. Finally, through absorption of a ferrofluid on the porous PVDFmembrane, the proposed ferro-actuator using porous PVDFmembranes with different porosities was fabricated. We executed the characterization and actuation test as follows. First, the silica size of the silica-embedded PVDFmembrane and the pore size of the porous PVDFmembrane were analyzed using scanning electron microscopy (SEM) imaging. Second, energy-dispersive x-ray spectroscopy analysis showed that the silica had clearly been removed from the silica-embedded PVDFmembrane by HF etching. Third, through x-ray photoelectron spectroscopy and vibrating sample magnetometer (VSM) of the ferro-actuators, we found that more ferrofluids were absorbed by the porous PVDFmembrane when the pore of the membrane was smaller and uniformly distributed. Finally, we executed tip displacement and a blocking force test of the proposed ferro-actuator using the porous PVDFmembrane. Similar to the VSM result, the ferro-actuator that used a porous PVDFmembrane with smaller pores exhibited better actuation performance. The ferro-actuator that used a porous PVDFmembrane displayed a tip displacement that was about 7.2-fold better and a blocking force that was about 6.5-fold better than the ferro-actuator that used a pure PVDFmembrane. Thus, we controlled the pore size of the porous PVDFmembrane and enhanced the actuation performance of the ferro-actuator using a porous PVDFmembrane.

This paper reports experiments using a flat-sheet module with 0.18 approximately 0.45 microm ePTFE (expanded polytetrafluoroethylene) and PVDF (polyvinylidene fluoride) membranes to show the effects of membrane properties, salt concentration and fluid hydrodynamics on the permeate flux and salt rejection of DCMD (direct contact membrane distillation). A theoretical prediction of the permeate flux was carried out, and was in close agreement with the experimental results. In addition, the energy integration of the process was also analyzed in order to evaluate module design to increase energy efficiency. According to the simulated results of the energy integration design, a combination of simultaneous cooling of the permeate stream and an additional heat exchanger to lower the temperature of the permeate stream not only enhances the MD flux, but also reduces energy consumption. PMID:20651439

The preparation and physical characterization of a poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid) (PVDF-g-PSSA) membrane prepared by a solution-grafting method were described. These membranes exhibited high conductivity with a value 3.22 x 10(-2) S/cm at 30 degrees C. ICP studies revealed that the PVDF-g-PSSA membrane showed dramatically lower vanadium ion permeability compared to Nafion 117. Trivalent vanadium ions had the highest permeability through all these membranes in contrast to pentavalent vanadium ions with the lowest. The VRB with the low-cost PVDF-g-PSSA membrane exhibited a higher performance than that with Nafion 117 under the same operating conditions, and its energy efficiency reached 75.8% at 30 mA/cm(2). The performance of VRB with the PVDF-g-PSSA membrane can be maintained after more than 200 cycles at a current density of 60 mA/cm(2). PMID:16853627

Improvements in battery technology are necessary as Li-ion batteries transition from consumer electronic to vehicular and industrial uses. An important bottle-neck in battery efficiency and safety is the quality of the separators, which prevent electric short-circuits between cathode and anode, while allowing an easy flow of ions between them. In this study, cellulose acetate was dissolved in a mixed solvent with poly(vinylpyrrolidone) (PVP), and the mixture was forcespun in a peudo paper making process to yield nanofibrillated nonwoven mats. The mats were soaked in NaOH/Ethanol to strip PVP and regenerate cellulose from its acetate precursor. The cellulose mats were then dipped in poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) to yield the cellulose/PVDF-HFP composte membranes. These membranes were characterized chemically through FTIR spectroscopy and solvent-stability tests, thermally through DSC, physically by stress/strain measurements along with weight-based electrolyte uptake, and electrically by AC-impedance spectroscopy combined with capacitative cycling.

A gel electrolyte membrane is obtained through the absorption of a carbamate-modified liquid disiloxane-containing lithium bis(trifluoromethane)sulfonimide (LiTFSI) by using macroporous poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) membranes. The porous membranes are prepared by means of a phase inversion technique. The resulting gel electrolyte membrane is studied by using differential scanning calorimetry, Fourier-transform infrared (FTIR) spectroscopy, and microscope mapping through coherent anti-Stokes Raman scattering (CARS) confocal microscopy and impedance spectroscopy. The ionic conductivity of the gel electrolyte is 10(-4) S cm(-1) at 20 °C. FTIR spectroscopy reveals interactions between LiTFSI and the carbonyl moiety of the disiloxane. No interactions between LiTFSI and PVDF-HFP or between disiloxane and PVDF-HFP are detected by FTIR spectroscopy. Furthermore, the distribution of the α and β/γ phases of PVDF-HFP and the homogeneous distribution of disiloxane/LiTFSI in the gel electrolyte membranes are examined by FTIR mapping. CARS confocal microscopy is used to image the three-dimensional interconnectivity, which reveals a reticulated structure of macrovoids in the porous PVDF-HFP framework. Owing to properties such as electrochemical and thermal stability of the disiloxane-based liquid electrolyte and the mechanical stability of the porous PVDF-HFP membrane, the gel electrolyte membranes presented herein are promising candidates for applications as electrolytes/separators in lithium-ion batteries. PMID:24737746

Polyvinylidene fluoride (PVDF)/polymethylmethacrylate (PMMA)/thermoplastic polyurethane (TPU) blend hollow fiber membranes were successfully prepared by the wet-spinning method with the loading of PMMA and TPU in a range of polymer concentrations varying from 0 to 20 wt% and at a total polymer concentration of 16 wt%. The influence of the addition of PMMA and TPU on the morphologies and the properties of such prepared membranes was investigated through FTIR-ATR, SEM, viscosity measurements, UF experiments and mechanical strength tests. Based on the experimental results, the compatibility of the PVDF, PMMA and TPU blend was best under the conditions of the PVDF-rich phase. The elongation at break of the membrane increased to a maximum of 146% with increase in the TPU concentration to 20 wt% in dope solution. The addition of PMMA increased the water permeation flux from 120 to 195 L/(m(2) h) initially. The flux then decreased when PMMA concentration was increased to over 10 wt%. The membranes obtained at optimized blending ratio were applied to the dyeing process wastewater filtration. During continuous filtration for 8 h, the flux was stabilized at about 20 L/(m(2) h) at 0.1 MPa. The reduction in COD(Cr), turbidity and color were about 63, 84 and 63% respectively. PMID:22378000

We propose a novel strategy for narrowing down the pore size distribution of ready-made nanofiltration membranes (NFMs) via pore wall modification. NFMs were subjected to the filtration of a highly reactive molecule solution, during which large pores were selectively reduced in size. The as-treated NFMs have high monovalent ion/divalent ion selectivity. PMID:27321407

The purpose of this study was to develop a membrane for guided tissue regeneration applicable in periodontology that could release antimicrobial agent during the healing period. Our strategy consisted to graft beta-cyclodextrin (beta-CD), a molecule that is known to form inclusion complexes with a large variety of drugs, onto PVDFmembranes. Grafting occurred by using citric acid that provoked a crosslinking reaction of beta-CD, and the resulting polymer was imprisoned into the porous structure of the PVDFmembrane. The reaction produced a weight increase of the membrane, the range of which depended on the temperature and on the time of curing applied in the process. The biological behavior of the membranes evaluated by proliferation and vitality tests showed good proliferation and improved activity of L132 epithelial cells on the raw and on the grafted membranes. Doxycyclin (DOX) and chlorhexidine (CHX) were used as antimicrobial agents. Their inclusion into the beta-CD cavity in aqueous solutions was confirmed by NMR spectroscopy. After the impregnation of the membranes with DOX and CHX, their release was studied in vitro in batch type experiments and measured by UV spectrophotometry. Low amounts of DOX and CHX were delivered from the raw membranes within the first few hours of tests. Grafted membranes, however, delivered DOX and CHX in larger quantities within 24 h and 10 days respectively. PMID:16758457

Using a liquid-solid phase inversion method, a hybrid matrix poly(vinylidene fluoride) (PVDF) membrane was prepared with alumina (Al2O3) nanoparticle addition. Pd/Fe nanoparticles (NPs) were successfully immobilized on the Al2O3/PVDFmembrane, which was characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The micrographs showed that the Pd/Fe NPs were dispersed homogeneously. Several important experimental parameters were optimized, including the mechanical properties, contact angle and surface area of Al2O3/PVDF composite membranes with different Al2O3 contents. At the same time, the ferrous ion concentration and the effect of hydrophilization were studied. The results showed that the modified Al2O3/PVDFmembrane functioned well as a support. The Al2O3/PVDFmembrane with immobilized Pd/Fe NPs exhibited high efficiency in terms of dichloroacetic acid (DCAA) dechlorination. Additionally, a reaction pathway for DCAA dechlorination by Pd/Fe NPs immobilized on the Al2O3/PVDFmembrane system was proposed. PMID:25968273

Once formed, fusion pores rapidly enlarge to semi-stable conductance values. The membranes lining the fusion pore are continuous bilayer structures, so variations of conductance in time reflect bending and stretching of membranes. We therefore modeled the evolution of fusion pores using the theory of the mechanics of deforming homogeneous membranes. We calculated the changes in length and width of theoretical fusion pores according to standard dynamical equations of motion. Theoretical fusion pores quickly achieve semi-stable dimensions, which correspond to energy minima located in a canyon between energy barriers. The height of the barrier preventing pore expansion diminishes along the dimensions of length and width. The bottom of the canyon slopes gently downward along increasing length. As a consequence, theoretical fusion pores slowly lengthen and widen as the dimensions migrate along the bottom of the canyon, until the barrier vanishes and the pore rapidly enlarges. The dynamics of growth is sensitive to tension, spontaneous curvature, bending elasticity, and mobilities. This sensitivity can account for the quantitative differences in pore evolution observed in two experimental systems: HA-expressing cells fusing to planar bilayer membranes and beige mouse mast cell degranulation. We conclude that the mechanics of membranes could cause the phenomenon of stagewise growth of fusion pores. Images FIGURE 9 PMID:8599655

Antibodies directed against ribonucleoprotein (RNP) particles are observed in systemic lupus erythematosus. Ro RNP particle is one such target. It is composed of a 60 kDa protein (Ro 60 or SS-A) that is non-covalently associated with at least one of the four short uridine-rich RNAs (the hY RNAs). Previously, we showed that multiple antigenic peptides (MAPs) made from the sequence of the Ro 60 autoantigen could be used, using double-immunodiffusion studies, enzyme-linked immunosorbant assay, affinity chromatography, and surface plasmon resonance, to show intramolecular and intermolecular protein-protein interaction within the Ro 60 RNP particle. We also observed that calcium is important in mediating this interaction. We hypothesized, therefore, that 60 kDa Ro is a calcium-binding protein. To investigate this, we electrophoresed 60 kDa Ro MAPs, transferred them to PVDFmembrane, and assayed calcium binding using the Quin-2 system. Several Ro 60 MAPs were found to bind calcium using this assay, as well as bovine serum albumin, another calcium-binding protein. However, a MAP constructed from the Sm autoantigen did not bind to calcium. These data, along with our observation regarding the involvement of calcium in protein-protein interaction occurring between Ro 60 antigen and Ro 60 MAPs, makes us propose that Ro 60 antigen is a calcium-binding protein. PMID:26139264

Pre-treatment is normally required to reduce or control the fouling of ultrafiltration (UF) membranes in drinking water treatment process. Current pre-treatment methods, such as coagulation, are only partially effective to prevent long-term fouling. Since biological activities are a major contributor to accumulated fouling, the application of an oxidation/disinfection step can be an effective complement to coagulation. In this study, a novel pre-treatment method has been evaluated at laboratory scale consisting of the addition of low dose ozone into the UF membrane tank after coagulation and the use of a hollow-fibre membrane coated with/without MnO2 nanoparticles over a test period of 70 days. The results showed that there was minimal fouling of the MnO2 coated membrane (0.5 kPa for 70 days), while the uncoated membrane experienced both reversible and irreversible fouling. The difference was attributed to the greatly reduced presence of bacteria and organic matter because of the catalytic decomposition of ozone to hydroxyl radicals and increase of the hydrophilicity of the membrane surface. In particular, the MnO2 coated membrane had a much thinner cake layer, with significantly less polysaccharides and proteins, and much less accumulated organic matter within the membranepores. PMID:27436142

Pre-treatment is normally required to reduce or control the fouling of ultrafiltration (UF) membranes in drinking water treatment process. Current pre-treatment methods, such as coagulation, are only partially effective to prevent long-term fouling. Since biological activities are a major contributor to accumulated fouling, the application of an oxidation/disinfection step can be an effective complement to coagulation. In this study, a novel pre-treatment method has been evaluated at laboratory scale consisting of the addition of low dose ozone into the UF membrane tank after coagulation and the use of a hollow-fibre membrane coated with/without MnO2 nanoparticles over a test period of 70 days. The results showed that there was minimal fouling of the MnO2 coated membrane (0.5 kPa for 70 days), while the uncoated membrane experienced both reversible and irreversible fouling. The difference was attributed to the greatly reduced presence of bacteria and organic matter because of the catalytic decomposition of ozone to hydroxyl radicals and increase of the hydrophilicity of the membrane surface. In particular, the MnO2 coated membrane had a much thinner cake layer, with significantly less polysaccharides and proteins, and much less accumulated organic matter within the membranepores. PMID:27436142

Pre-treatment is normally required to reduce or control the fouling of ultrafiltration (UF) membranes in drinking water treatment process. Current pre-treatment methods, such as coagulation, are only partially effective to prevent long-term fouling. Since biological activities are a major contributor to accumulated fouling, the application of an oxidation/disinfection step can be an effective complement to coagulation. In this study, a novel pre-treatment method has been evaluated at laboratory scale consisting of the addition of low dose ozone into the UF membrane tank after coagulation and the use of a hollow-fibre membrane coated with/without MnO2 nanoparticles over a test period of 70 days. The results showed that there was minimal fouling of the MnO2 coated membrane (0.5 kPa for 70 days), while the uncoated membrane experienced both reversible and irreversible fouling. The difference was attributed to the greatly reduced presence of bacteria and organic matter because of the catalytic decomposition of ozone to hydroxyl radicals and increase of the hydrophilicity of the membrane surface. In particular, the MnO2 coated membrane had a much thinner cake layer, with significantly less polysaccharides and proteins, and much less accumulated organic matter within the membranepores.

High modulus poly(p-phenylene terephtalamide) (PPTA) reinforced composites are of great scientific interests. But the thermodynamic difference makes the polymer pairs incompatible and endows the composites with inferior physical-chemical properties. In this study, hydrophilic poly(vinylidene fluoride) (PVDF)/poly(p-phenylene terephtalamide) (PPTA) blend membrane with improved hydrophilicity and mechanical strength was prepared through in situ polycondensation of p-phenylene diamine (PPD) and terephthaloyl chloride (TPC) in PVDF solution and subsequent immersion precipitation phase inversion process. The effects of PPTA concentration in polymer dopes on membrane formation process, structure, morphology and performance were systematically investigated. The results showed that thermodynamically, PPTA acted as a demixing enhancer which accelerated the phase inversion process. Dynamically, liquid-liquid phase separation was still in control of membrane formation process especially in the later period, whereas the addition of PPTA mainly promoted the early emergence of the liquid-liquid demixing. The surface hydrophilicity, ant-fouling properties and mechanical strength were significantly improved when PPTA content was 17 wt%. When PPTA content increased to 26 wt%, membrane bursting pressure increased to nearly 0.6 MPa which was 1.5 times higher than that of PVDFmembrane. The resultant PVDF/PPTA blend membrane exhibited an improved antifouling property than that of PVDFmembrane when applied in the MBR in the treatment of landfill leachate and also showed a relatively high removal rate of chemical oxygen demand (COD) and chrom.

Formation of channel-like pores in a plant membrane was induced within seconds after application of an aqueous solution containing regurgitant of the insect larvae Spodoptera littoralis. Gated pore currents recorded on the tonoplast of the Charophyte Chara corallina displayed conductances up to several hundred pS. A voltage-dependent gating reaction supports the assumption that pore-forming molecules have amphipathic properties. Regurgitant samples separated into masses smaller or larger than 3kDa were evaluated by patch-clamp and mass spectroscopy. Fractions containing peptides larger than 3kDa constituted pores of large conductances, peptides smaller than 3kDa constituted pores of small conductances. Peptide-free eluates did not constitute conducting pores, indicating that pore-forming components in regurgitant are membrane-spanning oligopeptides. PMID:17967419

We demonstrate here a new electrokinetic phenomenon, Electroosmotic flow (EOF) rectification, in synthetic membranes containing asymmetric pores. Mica membranes with pyramidally shaped pores prepared by the track-etch method were used. EOF was driven through these membranes by using an electrode in solutions on either side to pass a constant ionic current through the pores. The velocity of EOF depends on the polarity of the current. A high EOF velocity is obtained when the polarity is such that EOF is driven from the larger base opening to the smaller tip opening of the pore. A smaller EOF velocity is obtained when the polarity is reversed such that EOF goes from tip to base. We show that this rectified EOF phenomenon is the result of ion current-rectification observed in such asymmetric-poremembranes.

Biological cells and their organelles are protected by ultra thin membranes. These membranes accomplish a broad variety of important tasks like separating the cell content from the outer environment, they are the site for cell-cell interactions and many enzymatic reactions, and control the in- and efflux of metabolites. For certain physiological functions e.g. in the fusion of membranes and also in a number of biotechnological applications like gene transfection the membrane integrity needs to be compromised to allow for instance for the exchange of polar molecules across the membrane barrier. Mechanisms enabling the transport of molecules across the membrane involve membrane proteins that form specific pores or act as transporters, but also so-called lipid pores induced by external fields, stress, or peptides. Recent progress in the simulation field enabled to closely mimic pore formation as supposed to occur in vivo or in vitro. Here, we review different simulation-based approaches in the study of membranepores with a focus on lipid pore properties such as their size and energetics, poration mechanisms based on the application of external fields, charge imbalances, or surface tension, and on pores that are induced by small molecules, peptides, and lipids. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg. PMID:26748016

A method is disclosed for the production of metal oxide ceramic membranes of very small pore size. The process is particularly useful in the creation of titanium and other transition metal oxide membranes. The method utilizes a sol-gel process in which the rate of particle formation is controlled by substituting a relatively large alcohol in the metal alkoxide and by limiting the available water. Stable, transparent metal oxide ceramic membranes are created having a narrow distribution of pore size, with the pore diameter being manipulable in the range of 5 to 40 Angstroms.

A method is disclosed for the production of metal oxide ceramic membranes of very small pore size. The process is particularly useful in the creation of titanium and other transition metal oxide membranes. The method utilizes a sol-gel process in which the rate of particle formation is controlled by substituting a relatively large alcohol in the metal alkoxide and by limiting the available water. Stable, transparent metal oxide ceramic membranes are created having a narrow distribution of pore size, with the pore diameter being manipulable in the range of 5 to 40 Angstroms.

AC (sinusoidal) fields with frequencies from kilohertz to gigahertz have been used for gene delivery. To understand the impact of AC fields on electroporation dynamics, we couple a nondimensionalized Smoluchowski equation to an exact representation of the cell membrane voltage obtained solving the Laplace equation. The slope of the pore energy function, dφ/dr, with respect to pore radius is critical in predicting pore dynamics in AC fields because it can vary from positive, inducing pore shrinkage, to negative, driving pore growth. Specifically, the net sign of the integral of dφ/dr over time determines whether the average pore size grows (negative), shrinks (positive), or oscillates (zero) indefinitely about a steady-state radius, rss. A simple analytic relationship predicting the amplitude of the membrane voltage necessary for this behavior agrees well with simulation for frequencies from 500 kHz to 5 MHz for rss < 10 nm. For larger pore size (rss > 10 nm), dφ/dr oscillates about a negative value, suggesting that a net creation of pores may be necessary to maintain a constant pore size. In both scenarios, the magnitude of rss depends only upon the amplitude of the membrane voltage and not directly upon the applied field frequency other than the relationship between the amplitudes of the applied field and membrane voltage.

The mechanical behavior of lipid bilayers spanning the pores of highly ordered porous silicon substrates was scrutinized by local indentation experiments as a function of surface functionalization, lipid composition, solvent content, indentation velocity, and pore radius. Solvent-containing nano black lipid membranes (nano-BLMs) as well as solvent-free pore-spanning bilayers were imaged by fluorescence and atomic force microscopy prior to force curve acquisition, which allows distinguishing between membrane-covered and uncovered pores. Force indentation curves on pore-spanning bilayers attached to functionalized hydrophobic porous silicon substrates reveal a predominately linear response that is mainly attributed to prestress in the membranes. This is in agreement with the observation that indentation leads to membrane lysis well below 5% area dilatation. However, membrane bending and lateral tension dominate over prestress and stretching if solvent-free supported membranes obtained from spreading giant liposomes on hydrophilic porous silicon are indented. An elastic regime diagram is presented that readily allows determining the dominant contribution to the mechanical response upon indentation as a function of load and pore radius. PMID:19453196

Melittin is a prototype of the ubiquitous antimicrobial peptides that induce pores in membranes. It is commonly used as a molecular device for membrane permeabilization. Even at concentrations in the nanomolar range, melittin can induce transient pores that allow transmembrane conduction of atomic ions but not leakage of glucose or larger molecules. At micromolar concentrations, melittin induces stable pores allowing transmembrane leakage of molecules up to tens of kilodaltons, corresponding to its antimicrobial activities. Despite extensive studies, aspects of the molecular mechanism for pore formation remain unclear. To clarify the mechanism, one must know the states of the melittin-bound membrane before and after the process. By correlating experiments using giant unilamellar vesicles with those of peptide-lipid multilayers, we found that melittin bound on the vesicle translocated and redistributed to both sides of the membrane before the formation of stable pores. Furthermore, stable pores are formed only above a critical peptide-to-lipid ratio. The initial states for transient and stable pores are different, which implies different mechanisms at low and high peptide concentrations. To determine the lipidic structure of the pore, the pores in peptide–lipid multilayers were induced to form a lattice and examined by anomalous X-ray diffraction. The electron density distribution of lipid labels shows that the pore is formed by merging of two interfaces through a hole. The molecular property of melittin is such that it adsorbs strongly to the bilayer interface. Pore formation can be viewed as the bilayer adopting a lipid configuration to accommodate its excessive interfacial area. PMID:23940362

Pore forming toxins (PFTs) evolved to permeate the plasma membrane of target cells. This is achieved in a multistep mechanism that usually involves binding of soluble protein monomer to the lipid membrane, oligomerization at the plane of the membrane, and insertion of part of the polypeptide chain across the lipid membrane to form a conductive channel. Introduced pores allow uncontrolled transport of solutes across the membrane, inflicting damage to the target cell. PFTs are usually studied from the perspective of structure-function relationships, often neglecting the important role of the bulk membrane properties on the PFT mechanism of action. In this Account, we discuss how membrane lateral heterogeneity, thickness, and fluidity influence the pore forming process of PFTs. In general, lipid molecules are more accessible for binding in fluid membranes due to steric reasons. When PFT specifically binds ordered domains, it usually recognizes a specific lipid distribution pattern, like sphingomyelin (SM) clusters or SM/cholesterol complexes, and not individual lipid species. Lipid domains were also suggested to act as an additional concentration platform facilitating PFT oligomerization, but this is yet to be shown. The last stage in PFT action is the insertion of the transmembrane segment across the membranes to build the transmembrane pore walls. Conformational changes are a spontaneous process, and sufficient free energy has to be available for efficient membrane penetration. Therefore, fluid bilayers are permeabilized more readily in comparison to highly ordered and thicker liquid ordered lipid phase (Lo). Energetically more costly insertion into the Lo phase can be driven by the hydrophobic mismatch between the thinner liquid disordered phase (Ld) and large protein complexes, which are unable to tilt like single transmembrane segments. In the case of proteolipid pores, membrane properties can directly modulate pore size, stability, and even selectivity. Finally

This paper demonstrates a microfluidic chip for multiple immunoassays on electrospun (ES) nanofibrous membranes made of PVDF. This microchip enables the detection of multiple pairs of protein-protein interactions in one experiment by crossing parallel arrays of microchannels. This chip uses ESPVDF membrane with high specific surface area as the substrate to adsorb protein for immobilized immunoassays so that increased levels of protein adsorption may lower the LOD in immunoassays. We employ a simple and effective method for chip assembly by scotch tape to incorporate the ESPVDF membrane into the microchip. We believe that the present work will facilitate the development of methods for the on-site diagnosis of diseases whose detection is based on antigen-antibody recognition, and improve the efficiencies of certain experiments that need to identify tens to hundreds of protein-protein interactions with relatively low cost in the future. PMID:19722208

Fabrication of fouling resistant UF membranes requires the use of hydrophilic polymer additives that must be trapped in the polymer matrix during the phase separation processing. The knowledge of the polymeric additive distribution across the whole thickness should help to the design of more efficient membranes. This paper aims at developing a new methodology based on Raman microscopy spectroscopy owing to its high spatial resolution. A UF hollow fiber made from a blend of PVDF as polymer matrix and PVP as additive was chosen as a model membrane for this study. The PVP concentration profile along the cross-section radial axis was determined by using two ways of spectrum treatment including the analytical method by the peak intensity ratio calculation and a multivariate analysis with a partial least-squares regression model. The feasibility of the two approaches was discussed.

Lead contamination is one of the most serious problems in drinking water facing humans. In this study, a novel zirconium phosphate modified polyvinyl alcohol (PVA)-PVDFmembrane was developed for lead removal. The zirconium ions and PVA were firstly coated onto a PVDFmembrane through crosslinking reactions with glutaraldehyde, which was then modified by phosphate. The adsorption kinetics study showed that most of ultimate uptake occurred in 5 h. The adsorption increased with an increase in pH; the optimal adsorption was achieved at pH 5.5. The experimental data were better described by Langmuir equation than Freundlich equation; the maximum adsorption capacity was 121.2 mg-Pb/g at pH 5.5, much higher than other reported adsorptive membranes. The membrane exhibited a higher selectivity for lead over zinc with a relative selectivity coefficient (Pb(2+)/Zn(2+)) of 9.92. The filtration study showed that the membrane with an area of 12.56 cm(2) could treat 13.9 L (equivalent to 73,000 bed volumes) of lead containing wastewater with an influent concentration of 224.5 μ g/L to meet the maximum contaminant level of 15 μ g/L. It was demonstrated that the membrane did well in the removal of lead in both simulated wastewater and lead-spiked reservoir water and had a good reusability in its applications. The XPS studies revealed that the lead uptake was mainly due to cation exchange between hydrogen ions and lead ions. PMID:27311109

By a radiation-induced grafting technique, we have functionalized track-etched nanoporous polymer membranes with mercury sensitive poly-4-vinyl pyridine (P4VP). Coating of these membranes with a very thin layer of gold results in an electrochemical sensor that is very selective and highly sensitive for mercury LOD 5 ng/L - well below the norms for water (0.015 μg/L potable water and 0.5 μg/L residual waters-French water norms of 27 October 2011). E-beam irradiation permitted optimization of the radiografting synthesis on PVDF thin films prior to ion-track grafting. Synthesis and characterization by EPR, FESEM and FTIR are described in detail. A comparison between FTIR in ATR and transmission modes enabled us to localize the grafting on the surface of the e-beam irradiated PVDF films allowing us to extrapolate what happens on the etched tracks. Using Square Wave Anodic Stripping Voltammetry (SW-ASV), mercury concentrations of 1 μg/L are detected in 2 h and low ng/L concentrations are detected after 24 h of adsorption. The adsorption is passive so sensors do not require instrumentation and the analysis takes only 3-4 min. Also, the P4VP functionalized sensor appears insensitive to pH variations (pHs 3-9), high salt concentrations (up to 1 g/L) and the presence of other heavy metals in the same solution.

Pore-forming proteins (PFPs) interact with lipid bilayers to compromise membrane integrity. Many PFPs function by inserting a ring of oligomerized subunits into the bilayer to form a protein-lined hydrophilic channel. However, mounting evidence suggests that PFPs can also generate 'proteolipidic' pores by contributing to the fusion of inner and outer bilayer leaflets to form a toroidal structure. We discuss here toroidal pore formation by peptides including melittin, protegrin, and Alzheimer's Aβ1-41, as well as by PFPs from several evolutionarily unrelated families: the colicin/Bcl-2 grouping including the pro-apoptotic protein Bax, actinoporins derived from sea anemones, and the membrane attack complex-perforin/cholesterol dependent cytolysin (MACPF/CDC) set of proteins. We also explore how the structure and biological role of toroidal pores might be investigated further. PMID:25440714

Provided herein composition and methods for nanoporous membranes comprising single walled, double walled, or multi-walled carbon nanotubes embedded in a matrix material. Average pore size of the carbon nanotube can be 6 nm or less. These membranes are a robust platform for the study of confined molecular transport, with applications in liquid and gas separations and chemical sensing including desalination, dialysis, and fabric formation.

Several experimental methods have been developed to study the mechanical response of vesicles under an applied tension. Of particular note are the micropipette aspiration techniques and the use of a viscous solution to extend the lifetime of pores. MD simulations have also been used to study the energetic and structural properties of these transient pores on a molecular level. However, they often require extremely high tensions beyond the regime where pore formation is a thermally-activated event. We approach the nucleation problem by combining the string method with dynamic self-consistent field (DSCF) theory to obtain the full minimum energy path (MEP) to pore formation for a range of surface tensions γ . We compare our results with classical nucleation theory (CNT). Near the coexistence (γ --> 0) the rim of the pore is well-defined and the line tension is well approximated by the macroscopic definition given by CNT. However, when the free energy barrier is within ~ 10 kT , the transition state is somewhere between a stalk-like structure and a thinned membrane leading to a hole that is partially exposed to solvents. These molecular rearrangements involved in the formation of a pore are not captured by CNT.

Despite a growing interest in conducting polymer based actuators, a robust fabrication technique is still needed. We suggest a fabrication method that allows fast production of conducting polymer actuators from commercially available polyvinylidene flouride membranes (PVDF) and a PEDOT/PSS solution. In order to improve adhesion of those materials, Ar plasma induced grafting is used to create hydrophilic surfaces of up to 40 μm. Hydrophilic PVDF-graft-polyethylene glycol allows diffusion of PEDOT/PSS in the pores of the membranes, while hydrophobic middle layers prevent short circuits. In this way, soft actuators can be fabricated by consequent drop casting and drying of conducting polymer.

Integration of solid-state biosensors and lipid bilayer membranes is important for membrane protein research and drug discovery. In these sensors, it is critical that the solid-state sensing material does not have adverse effects on the conformation or functionality of membrane-bound molecules. In this work, pore-spanning lipid membranes are formed over an array of periodic nanopores in free-standing gold films for surface plasmon resonance (SPR) kinetic binding assays. The ability to perform kinetic assays with a transmembrane protein is demonstrated with α-hemolysin (α-HL). The incorporation of α-HL into the membrane followed by specific antibody binding (anti-α-HL) red-shifts the plasmon resonance of the gold nanopore array, which is optically monitored in real time. Subsequent fluorescence imaging reveals that the antibodies primarily bind in nanopore regions, indicating that α-HL incorporation preferentially occurs into areas of pore-spanning lipid membranes. PMID:21218136

Amyloid (A β) peptide contributes to Alzheimer's disease by a yet unidentified mechanism. One of the possible mechanisms of A β toxicity is formation of pores in cellular membranes. We have characterized the formation of pores in phospholipid membranes by the Aβ25 - 35 peptide (GSNKGAIIGLM) using fluorescence, Fourier transform infrared spectroscopy (FTIR) and circular dichroism (CD) techniques. CD and FTIR identified formation of β-sheet structure upon incubation of the peptide in aqueous buffer for 2 hours. Unilamellar vesicles composed of a zwitterionic lipid, 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC), and 70 % POPC plus 30 % of an acidic lipid, 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG), are made in 30 mM CaCl2. Quin-2, a fluorophore that displays increased fluorescence upon Ca2+ binding, is added to the vesicles externally. Peptide addition results in increased Quin-2 fluorescence, which is interpreted by binding of the peptide to the vesicles, pore formation, and Ca2+ leakage. The positive and negative control measurements involve addition of a detergent, Triton X-100, which causes vesicle rupture and release of total calcium, and blank buffer, respectively.

The transport rate of molecules through polymeric membranes is normally limited because of their micrometer-scale thickness which restricts their suitability for more practical application. To study the effect of effective pore length on the transport behavior, polymer membranes containing cylindrical and asymmetric-shaped nanopores were prepared through a two-step ion track-etching technique. Permeation experiments were performed separately to investigate the transport properties (molecular flux and selectivity) of these track-etched membranes. The permeation data shows that the molecular flux across membranes containing asymmetric nanopores is higher compared to those having cylindrical pores. On the other hand, the cylindrical poremembranes exhibit higher selectivity than asymmetric pores for the permeation of charged molecules across the membrane. Current-voltage (I-V) measurements of single-poremembranes further verify that asymmetric pores exhibit lower resistance for the flow of ions and therefore show higher currents than cylindrical pores. Moreover, unmodified and polyethyleneimine (PEI) modified asymmetric-shaped poremembranes were successfully used for the separation of cationic and anionic analyte molecules from their mixture, respectively. In this study, two distinct effects (pore geometry and pore density, i.e. number of pores cm-2), which mainly influence membrane selectivity and molecular transport rates, were thoroughly investigated in order to optimize the membrane performance. In this context, we believe that membranes with high molecular transport rates could readily find their application in molecular separation and controlled drug delivery processes.

The transport rate of molecules through polymeric membranes is normally limited because of their micrometer-scale thickness which restricts their suitability for more practical application. To study the effect of effective pore length on the transport behavior, polymer membranes containing cylindrical and asymmetric-shaped nanopores were prepared through a two-step ion track-etching technique. Permeation experiments were performed separately to investigate the transport properties (molecular flux and selectivity) of these track-etched membranes. The permeation data shows that the molecular flux across membranes containing asymmetric nanopores is higher compared to those having cylindrical pores. On the other hand, the cylindrical poremembranes exhibit higher selectivity than asymmetric pores for the permeation of charged molecules across the membrane. Current-voltage (I-V) measurements of single-poremembranes further verify that asymmetric pores exhibit lower resistance for the flow of ions and therefore show higher currents than cylindrical pores. Moreover, unmodified and polyethyleneimine (PEI) modified asymmetric-shaped poremembranes were successfully used for the separation of cationic and anionic analyte molecules from their mixture, respectively. In this study, two distinct effects (pore geometry and pore density, i.e. number of pores cm(-2)), which mainly influence membrane selectivity and molecular transport rates, were thoroughly investigated in order to optimize the membrane performance. In this context, we believe that membranes with high molecular transport rates could readily find their application in molecular separation and controlled drug delivery processes. PMID:26553245

We recently proposed a cylindrical coat for the nuclear poremembrane in the nuclear pore complex (NPC). This scaffold is generated by multiple copies of seven nucleoporins. Here, we report three crystal structures of the nucleoporin pair Seh1{center_dot}Nup85, which is part of the coat cylinder. The Seh1{center_dot}Nup85 assembly bears resemblance in its shape and dimensions to that of another nucleoporin pair, Sec13{center_dot}Nup145C. Furthermore, the Seh1{center_dot}Nup85 structures reveal a hinge motion that may facilitate conformational changes in the NPC during import of integral membrane proteins and/or during nucleocytoplasmic transport. We propose that Seh1{center_dot}Nup85 and Sec13{center_dot}Nup145C form 16 alternating, vertical rods that are horizontally linked by the three remaining nucleoporins of the coat cylinder. Shared architectural and mechanistic principles with the COPII coat indicate a common evolutionary origin and support the notion that the NPC coat represents another class of membrane coats.

Disruption of cell membranes by Aβ is believed to be one of the key components of Aβ toxicity. However, the mechanism by which this occurs is not fully understood. Here, we demonstrate that membrane disruption by Aβ occurs by a two-step process, with the initial formation of ion-selective pores followed by nonspecific fragmentation of the lipid membrane during amyloid fiber formation. Immediately after the addition of freshly dissolved Aβ(1-40), defects form on the membrane that share many of the properties of Aβ channels originally reported from single-channel electrical recording, such as cation selectivity and the ability to be blockaded by zinc. By contrast, subsequent amyloid fiber formation on the surface of the membrane fragments the membrane in a way that is not cation selective and cannot be stopped by zinc ions. Moreover, we observed that the presence of ganglioside enhances both the initial pore formation and the fiber-dependent membrane fragmentation process. Whereas pore formation by freshly dissolved Aβ(1-40) is weakly observed in the absence of gangliosides, fiber-dependent membrane fragmentation can only be observed in their presence. These results provide insights into the toxicity of Aβ and may aid in the design of specific compounds to alleviate the neurodegeneration of Alzheimer's disease. PMID:22947931

We present a modeling approach to determine the permeability-selectivity tradeoff for microfiltration and ultrafiltration membranes with a distribution of pore sizes and pore shapes. Using the formulated permeability-selectivity model, the effect of pore aspect ratio and pore size distribution on the permeability-selectivity tradeoff of the membrane is analyzed. A finite element model is developed to study the effect of membrane stretching on the distribution of pore sizes and shapes in the stretched membrane. The effect of membrane stretching on the permeability-selectivity tradeoff of membranes is also analyzed. The results show that increasing pore aspect ratio improves membrane performance while increasing the width of pore size distribution deteriorates the performance. It was also found that the effect of membrane stretching on the permeability-selectivity tradeoff is greatly affected by the uniformity of pore distribution in the membrane. Stretching showed a positive shift in the permeability-selectivity tradeoff curve of membranes with well-dispersed pores while in the case of pore clustering, a negative shift in the permeability-selectivity tradeoff curve was observed. PMID:27509528

Indolicidin, a 13-residue cationic peptide with extremely high tryptophan content, exhibits broad-spectrum antimicrobial as well as hemolytic activity. To gain insight into the mechanism of indolicidin action on membrane permeability, liposome leakage induced by this peptide was studied by using various probes with vesicles of different lipid compositions. In liposomes containing negatively charged lipids, indolicidin induced rather unselective permeabilization. By contrast, the peptide appeared to be selective in provoking leakage of neutral, egg phosphatidylcholine (PC) liposomes: it effectively induced the release of negatively charged fluorescent dyes, carboxyfluorescein (CF), calcein and sulforhodamine B, but was unable to induce the leakage of a neutral compound, glucose, and that of positively charged doxorubicin. Moreover, organic anions, such as fatty acids, were found to suppress the indolicidin-induced CF leakage of egg PC liposomes. Based on these results, we concluded that indolicidin facilitates the dye release from uncharged lipid vesicles not by formation of membranepores as it is generally accepted for the majority of antimicrobial peptides but rather via translocation of dye molecules across the membrane in the form of dye-peptide complexes, i.e. indolicidin operates as an organic anion carrier. This conclusion was supported by observing the formation of complexes between indolicidin and pyrenebutyrate in solution. The indolicidin analog having only one arginine was ineffective in pyrenebutyrate binding and CF transport. The mode of action proposed here for indolicidin can be related to that previously postulated for oligoarginine derivatives which are able to carry organic anions across liposomal and bulk phase membranes [Sakai N. & Matile S. J. Am. Chem. Soc. 2003, 125:14348-14356]. The newly identified mechanism of peptide ionophoric activity in uncharged lipid membranes may be involved in hemolytic action of indolicidin via induction of

How the pro-apoptotic Bax protein permeabilizes the mitochondrial outer membrane is not fully understood. Previously, using cryo-electron microscopy (cryo-EM), we showed that activated Bax forms large, growing pores. Whether formed in liposomes or in mitochondrial outer membranes, Bax-induced pores exhibit the same morphology, with negative curvature flanking the edges and with no visible protein structure protruding from the membranes. Here we used cryo-EM to show that gold-labeled Bax molecules, after activation by Bid, became localized strictly at pore edges. This argues that Bax acts at short range to deform the membrane. Also, Bax molecules populated the walls of both small and large pores at the same density, implying that Bax is continuously recruited to the pores as they widen. Moreover, because all Bax molecules became oligomerized after membrane insertion, we infer that Bax oligomers are present at pore edges. We suggest that oligomerization may promote pore enlargement. PMID:27255832

How the pro-apoptotic Bax protein permeabilizes the mitochondrial outer membrane is not fully understood. Previously, using cryo-electron microscopy (cryo-EM), we showed that activated Bax forms large, growing pores. Whether formed in liposomes or in mitochondrial outer membranes, Bax-induced pores exhibit the same morphology, with negative curvature flanking the edges and with no visible protein structure protruding from the membranes. Here we used cryo-EM to show that gold-labeled Bax molecules, after activation by Bid, became localized strictly at pore edges. This argues that Bax acts at short range to deform the membrane. Also, Bax molecules populated the walls of both small and large pores at the same density, implying that Bax is continuously recruited to the pores as they widen. Moreover, because all Bax molecules became oligomerized after membrane insertion, we infer that Bax oligomers are present at pore edges. We suggest that oligomerization may promote pore enlargement. PMID:27255832

In this study, Fe (iron) and Ag (silver) based adsorbents were synthesized using solution combustion and in situ reduction techniques. The synthesized adsorbents were comprehensively characterized by different techniques including electron microscopy, BET, XRD, Zeta potential etc. Three chlorinated cationic dyes used were malachite green, methyl violet and pyronin Y. These dyes were adsorbed on various synthesized adsorbents [iron III oxide (Fe2O3)], iron III oxide decorated silver nanoparticles by combustion synthesis technique [Fe2O3–Ag(C)] and iron III oxide decorated silver nanoparticles using in situ reduction, [Fe2O3–Ag (S)]. The isotherm and the adsorption kinetics have been studied systematically. The kinetic data can be explained by the pseudo second order model and the adsorption equilibrium followed Langmuir isotherm. The equilibrium and kinetics results suggest that Fe2O3–Ag(S) nanoparticles showed the maximum adsorption among all the adsorbents. Hence, Polyvinylidene fluoride based membranes containing Fe2O3–Ag(S) nanoparticles were prepared via phase inversion (precipitation immersion using DMF/water) technique. The adsorption kinetics were studied in detail and it was observed that the composite membrane showed synergistic improvement in dye adsorption. Such membranes can be used for water purification.

Membrane fusion underlies multiple processes, including exocytosis of hormones and neurotransmitters. Membrane fusion starts with the formation of a narrow fusion pore. Radial expansion of this pore completes the process and allows fast release of secretory compounds, but this step remains poorly understood. Here we show that inhibiting the expression of the small GTPase Cdc42 or preventing its activation with a dominant negative Cdc42 construct in human neuroendocrine cells impaired the release process by compromising fusion pore enlargement. Consequently the mode of vesicle exocytosis was shifted from full-collapse fusion to kiss-and-run. Remarkably, Cdc42-knockdown cells showed reduced membrane tension, and the artificial increase of membrane tension restored fusion pore enlargement. Moreover, inhibiting the motor protein myosin II by blebbistatin decreased membrane tension, as well as fusion pore dilation. We conclude that membrane tension is the driving force for fusion pore dilation and that Cdc42 is a key regulator of this force. PMID:25143404

Bioprinting has a wide range of applications and significance, including tissue engineering, direct cell application therapies, and biosensor microfabrication. Recently, thermal inkjet printing has also been used for gene transfection. The thermal inkjet printing process was shown to temporarily disrupt the cell membranes without affecting cell viability. The transient pores in the membrane can be used to introduce molecules, which would otherwise be too large to pass through the membrane, into the cell cytoplasm. The application being demonstrated here is the use of thermal inkjet printing for the incorporation of fluorescently labeled g-actin monomers into cells. The advantage of using thermal ink-jet printing to inject molecules into cells is that the technique is relatively benign to cells. Cell viability after printing has been shown to be similar to standard cell plating methods. In addition, inkjet printing can process thousands of cells in minutes, which is much faster than manual microinjection. The pores created by printing have been shown to close within about two hours. However, there is a limit to the size of the pore created (~10 nm) with this printing technique, which limits the technique to injecting cells with small proteins and/or particles. A standard HP DeskJet 500 printer was modified to allow for cell printing. The cover of the printer was removed and the paper feed mechanism was bypassed using a mechanical lever. A stage was created to allow for placement of microscope slides and coverslips directly under the print head. Ink cartridges were opened, the ink was removed and they were cleaned prior to use with cells. The printing pattern was created using standard drawing software, which then controlled the printer through a simple print command. 3T3 fibroblasts were grown to confluence, trypsinized, and then resuspended into phosphate buffered saline with soluble fluorescently labeled g-actin monomers. The cell suspension was pipetted into the

Bioprinting has a wide range of applications and significance, including tissue engineering, direct cell application therapies, and biosensor microfabrication.1-10 Recently, thermal inkjet printing has also been used for gene transfection.8,9 The thermal inkjet printing process was shown to temporarily disrupt the cell membranes without affecting cell viability. The transient pores in the membrane can be used to introduce molecules, which would otherwise be too large to pass through the membrane, into the cell cytoplasm.8,9,11 The application being demonstrated here is the use of thermal inkjet printing for the incorporation of fluorescently labeled g-actin monomers into cells. The advantage of using thermal ink-jet printing to inject molecules into cells is that the technique is relatively benign to cells.8, 12 Cell viability after printing has been shown to be similar to standard cell plating methods1,8. In addition, inkjet printing can process thousands of cells in minutes, which is much faster than manual microinjection. The pores created by printing have been shown to close within about two hours. However, there is a limit to the size of the pore created (~10 nm) with this printing technique, which limits the technique to injecting cells with small proteins and/or particles. 8,9,11 A standard HP DeskJet 500 printer was modified to allow for cell printing.3, 5, 8 The cover of the printer was removed and the paper feed mechanism was bypassed using a mechanical lever. A stage was created to allow for placement of microscope slides and coverslips directly under the print head. Ink cartridges were opened, the ink was removed and they were cleaned prior to use with cells. The printing pattern was created using standard drawing software, which then controlled the printer through a simple print command. 3T3 fibroblasts were grown to confluence, trypsinized, and then resuspended into phosphate buffered saline with soluble fluorescently labeled g-actin monomers. The

In this study, polyvinylidene fluoride (PVDF) hollow-fiber hemodialysis membranes were prepared by non-solvent-induced phase separation. The PVDF hollow-fiber hemodialyzers were prepared by centrifugal casting. The results showed that the PVDFmembrane had better mechanical and separation properties when the membrane wall thickness was 40 μm and the N,N-dimethylacetamide in the core was 70 Vol%. Compared with commercial polysulfone hemodialysis membrane (Fresenius F60S membrane), the PVDFmembrane had better mechanical property and ultrafiltration (UF) flux of pure water. The PVDF dialyzer's removal efficiency for middle molecules was proven to be much higher than that of the F60S dialyzer. The UF coefficient of a high-flux PVDF dialyzer is 62.6 ml/h/mm Hg, whereas F60S is 42.5 ml/h/mm Hg, which can promote clearance for middle molecules. PMID:25781663

Transmembrane pores play an important role in various biophysical processes such as membrane permeation, membrane fusion, and antimicrobial peptide activity. In principal, all-atom molecular dynamics (MD) simulations provide an accurate model of pore formation in lipid membranes. However, the free energy landscape of transmembrane pore formation remains poorly understood, partly because potential of mean force (PMF) calculations of pore formation strongly depend on the choice of the reaction coordinate. In this study, we used umbrella sampling to compute PMFs for pore formation using three different reaction coordinates, namely, (i) a coordinate that steers the lipids in the lateral direction away from the pore center, (ii) the distance of a single lipid phosphate group from the membrane center, and (iii) the average water density inside a membrane-spanning cylinder. Our results show that while the three reaction coordinates efficiently form pores in membranes, they suffer from strong hysteresis between pore-opening and pore-closing simulations, suggesting that they do not restrain the systems close to the transition state for pore formation. The two reaction coordinates that act via restraining the lipids lead to more pronounced hysteresis compared with the coordinate acting on the water molecules. By comparing PMFs computed from membranes with different numbers of lipids, we observed significant artifacts from the periodic boundary conditions in small simulation systems. Further analysis suggests that the formation and disruption of a continuous hydrogen-bonding network across the membrane corresponds to the transition state for pore formation. Our study provides molecular insights into the critical steps of transmembrane pore formation, and it may guide the development of efficient reaction coordinates for pore formation. PMID:27254744

The productive fusion pore in membrane fusion is generally thought to be toroidally shaped. Theoretical studies and recent experiments suggest that its formation, in some scenarios, may be preceded by an initial pore formed near the rim of the extended hemifusion diaphragm (HD), a rim-pore. This rim-pore is characterized by a nontoroidal shape that changes with size. To determine this shape as well as the free energy along the pathway of rim-pore expansion, we derived a simple analytical free energy model. We argue that dilation of HD material via expansion of a rim-pore is favored over a regular, circular pore. Further, the expanding rim-pore faces a free energy barrier that linearly increases with HD size. In contrast, the tension required to expand the rim-pore decreases with HD size. Pore flickering, followed by sudden opening, occurs when the tension in the HD competes with the line energy of the rim-pore, and the rim-pore reaches its equilibrium size before reaching the critical pore size. The experimental observation of flickering and closing fusion pores (kiss-and-run) is very well explained by the observed behavior of rim-pores. Finally, the free energy landscape of rim-pore expansion/HD dilation may very well explain why some cellular fusion reactions, in their attempt to minimize energetic costs, progress via alternative formation and dilation of microscopic hemifusion intermediates. PMID:25418297

Conventional polymer membranes suffer from low flux and serious fouling when used for treating emulsified oil/water mixtures. Reported herein is the fabrication of a novel superhydrophilic and underwater superoleophobic poly(acrylic acid)-grafted PVDF filtration membrane using a salt-induced phase-inversion approach. A hierarchical micro/nanoscale structure is constructed on the membrane surface and endows it with a superhydrophilic/underwater superoleophobic property. The membrane separates both surfactant-free and surfactant-stabilized oil-in-water emulsions under either a small applied pressure (<0.3 bar) or gravity, with high separation efficiency and high flux, which is one to two orders of magnitude higher than those of commercial filtration membranes having a similar permeation property. The membrane exhibits an excellent antifouling property and is easily recycled for long-term use. The outstanding performance of the membrane and the efficient, energy and cost-effective preparation process highlight its potential for practical applications. PMID:24307602

Even though a number of different in vitro fusion assays have been developed to analyze protein mediated fusion, they still only partially capture the essential features of the in vivo situation. Here we established an in vitro fusion assay that mimics the fluidity and planar geometry of the cellular plasma membrane to be able to monitor fusion of single protein-containing vesicles. As a proof of concept, planar pore-spanning membranes harboring SNARE-proteins were generated on highly ordered functionalized 1.2 μm-sized pore arrays in Si3N4. Full mobility of the membrane components was demonstrated by fluorescence correlation spectroscopy. Fusion was analyzed by two color confocal laser scanning fluorescence microscopy in a time resolved manner allowing to readily distinguish between vesicle docking, intermediate states such as hemifusion and full fusion. The importance of the membrane geometry on the fusion process was highlighted by comparing SNARE-mediated fusion with that of a minimal SNARE fusion mimetic. PMID:26165860

Pore-forming proteins and peptides act on their targeted lipid bilayer membranes to increase permeability. This approach to the modulation of biological function is relevant to a great number of living processes, including; infection, parasitism, immunity, apoptosis, development and neurodegeneration. While some pore-forming proteins/peptides assemble into rings of subunits to generate discrete, well-defined pore-forming structures, an increasing number is recognised to form pores via mechanisms which co-opt membrane lipids themselves. Among these, membrane attack complex-perforin/cholesterol-dependent cytolysin (MACPF/CDC) family proteins, Bax/colicin family proteins and actinoporins are especially prominent and among the mechanisms believed to apply are the formation of non-lamellar (semi-toroidal or toroidal) lipidic structures. In this review I focus on the ways in which lipids contribute to pore formation and contrast this with the ways in which lipids are co-opted also in membrane fusion and fission events. A variety of mechanisms for pore formation that involve lipids exists, but they consistently result in stable hybrid proteolipidic structures. These structures are stabilised by mechanisms in which pore-forming proteins modify the innate capacity of lipid membranes to respond to their environment, changing shape and/or phase and binding individual lipid molecules directly. In contrast, and despite the diversity in fusion protein types, mechanisms for membrane fusion are rather similar to each other, mapping out a pathway from pairs of separated compartments to fully confluent fused membranes. Fusion proteins generate metastable structures along the way which, like long-lived proteolipidic pore-forming complexes, rely on the basic physical properties of lipid bilayers. Membrane fission involves similar intermediates, in the reverse order. I conclude by considering the possibility that at least some pore-forming and fusion proteins are evolutionarily related

The recent applications of nanosecond, megavolt-per-meter electric field pulses to biological systems show striking cellular and subcellular electric field induced effects and revive the interest in the biophysical mechanism of electroporation. We first show that the absolute rate theory, with experimentally based parameter input, is consistent with membranepore creation on a nanosecond time scale. Secondly we use a Smoluchowski equation-based model to formulate a self-consistent theoretical approach. The analysis is carried out for a planar cell membrane patch exposed to a 10ns trapezoidal pulse with 1.5ns rise and fall times. Results demonstrate reversible supraelectroporation behavior in terms of transmembrane voltage, pore density, membrane conductance, fractional aqueous area, pore distribution, and average pore radius. We further motivate and justify the use of Krassowska’s asymptotic electroporation model for analyzing nanosecond pulses, showing that pore creation dominates the electrical response and that pore expansion is a negligible effect on this time scale.

The formation of pores is an important process in cellular membranes. Here we use freestanding polymer films as model membranes to study the stability of nucleated pores. Polymer membranes with pores of varying size are patterned using a lithographic technique. The membranes are heated above their glass transition temperature to allow viscous flow to occur. Pores with a radius larger than a critical value grow, while pores smaller than the critical radius are observed to shrink and eventually close. Remarkably, holes that are close enough to the critical radius neither grow nor shrink, even though the film is in the melt state. A simple model which takes into account the energy cost of having additional surface area at the edge of a pore describes the experiments with no free parameters. Biological membranes have an additional energetic cost of forming a pore, which we mimic using a lamellar-forming diblock copolymer. Indeed, we find that the critical pore radius is increased when pore formation is frustrated by molecular architecture.

The innovative design and synthesis of nanofiber based hydro-philic/phobic membranes with a thin hydro-phobic nanofiber layer on the top and a thin hydrophilic nanofiber layer on the bottom of the conventional casted micro-porous layer which opens up a solution for membranepore wetting and improves the pure water flux in membrane distillation. PMID:25377488

The pore-forming antibacterial peptide magainin 2 was made divalent, tetravalent, and octavalent via a copper(I)-mediated 1-3 dipolar cycloaddition reaction ("click" chemistry). This series of pore-forming compounds was tested in vitro for their ability to form pores in large unilamillar vesicles (LUVs). A large increase in the pore-forming capability was especially observed with the tetravalent and octavalent magainin compounds in the LUVs consisting of DOPC, and the octavalent magainin compound showed a marked increase with the DOPC/DOPG LUVs. Activity was observed in the low nanomolar range for these compounds. PMID:17944489

Apolipoprotein L-I is the trypanolytic factor of human serum. Here we show that this protein contains a membranepore-forming domain functionally similar to that of bacterial colicins, flanked by a membrane-addressing domain. In lipid bilayer membranes, apolipoprotein L-I formed anion channels. In Trypanosoma brucei, apolipoprotein L-I was targeted to the lysosomal membrane and triggered depolarization of this membrane, continuous influx of chloride, and subsequent osmotic swelling of the lysosome until the trypanosome lysed.

Pore formation by membrane-active antimicrobial peptides is a classic strategy of pathogen inactivation through disruption of membrane biochemical gradients. It remains unknown why some membrane-active peptides also inhibit enveloped viruses, which do not depend on biochemical gradients. Here, we employ a label-free biosensing approach based on simultaneous quartz crystal microbalance-dissipation and ellipsometry measurements in order to investigate how a pore-forming, virucidal peptide destabilizes lipid vesicles in a surface-based experimental configuration. A key advantage of the approach is that it enables direct kinetic measurement of the surface-bound peptide-to-lipid (P:L) ratio. Comprehensive experiments involving different bulk peptide concentrations and biologically relevant membrane compositions support a unified model that membrane lysis occurs at or above a critical P:L ratio, which is at least several-fold greater than the value corresponding to the onset of pore formation. That is consistent with peptide-induced pores causing additional membrane strain that leads to lysis of highly curved membranes. Collectively, the work presents a new model that describes how peptide-induced pores may destabilize lipid membranes through a membrane strain-related lytic process, and this knowledge has important implications for the design and application of membrane-active peptides. PMID:26751083

A method for the production of metal oxide ceramic membranes is composed of very small pore size. The process is particularly useful in the creation of titanium and other transition metal oxide membranes. The method utilizes a sol-gel process in which the rate of particle formation is controlled by substituting a relatively large alcohol in the metal alkoxide and by limiting the available water. Stable, transparent metal oxide ceramic membranes are created having a narrow distribution of pore size, with the pore diameter being manipulable in the range of 5 to 40 Angstroms.

Pore-forming protein toxins possess the remarkable property that they can exist either in a stable water-soluble state or as an integral membranepore. In order to convert from the water-soluble to the membrane state, the toxin must undergo large conformational changes. Recent work on a class of pore-forming toxins that are rich in beta-sheet content suggests a common mechanism of membrane insertion may exist despite these toxins possessing very different primary, tertiary and quaternary structures. PMID:12893054

We present a theoretical study of the energetics, equilibrium size, and size distribution of membranepores composed of electrically charged amphipathic peptides. The peptides are modeled as cylinders (mimicking α-helices) carrying different amounts of charge, with the charge being uniformly distributed over a hydrophilic face, defined by the angle subtended by polar amino acid residues. The free energy of a pore of a given radius, R, and a given number of peptides, s, is expressed as a sum of the peptides' electrostatic charging energy (calculated using Poisson-Boltzmann theory), and the lipid-perturbation energy associated with the formation of a membrane rim (which we model as being semitoroidal) in the gap between neighboring peptides. A simple phenomenological model is used to calculate the membrane perturbation energy. The balance between the opposing forces (namely, the radial free energy derivatives) associated with the electrostatic free energy that favors large R, and the membrane perturbation term that favors small R, dictates the equilibrium properties of the pore. Systematic calculations are reported for circular pores composed of various numbers of peptides, carrying different amounts of charge (1–6 elementary, positive charges) and characterized by different polar angles. We find that the optimal R's, for all (except, possibly, very weakly) charged peptides conform to the “toroidal” pore model, whereby a membrane rim larger than ∼1 nm intervenes between neighboring peptides. Only weakly charged peptides are likely to form “barrel-stave” pores where the peptides essentially touch one another. Treating pore formation as a two-dimensional self-assembly phenomenon, a simple statistical thermodynamic model is formulated and used to calculate pore size distributions. We find that the average pore size and size polydispersity increase with peptide charge and with the amphipathic polar angle. We also argue that the transition of peptides from

A slit sieve model has been used to develop a general correlation between the average pore size of the upstream surface of a membrane and the molecular weight of the solute which it retains by better than 80%. The pore size is determined by means of the correlation using the high retention data from an ultrafiltration (UF) or a reverse osmosis (RO) experiment. The pore population density can also be calculated from the flux data via appropriate equations.

Experimental design and response surface methodology (RSM) were used to optimize the modification of conditions for glass surface grafting with acrylamide (AM) monomer for preparation of a glass fiber reinforced poly(vinylidene fluoride) (PVDF) composite membrane (GFRP-CM). The factors considered for experimental design were the UV (ultraviolet)-irradiation time, the concentrations of the initiator and solvent, and the kinds and concentrations of the silane coupling agent. The optimum operating conditions determined were UV-irradiation time of 25 min, an initiator concentration of 0-0.25 wt.%, solvent of N-Dimethylacetamide (DMAC), and silane coupling agent KH570 with a concentration of 7 wt.%. The obtained optimal parameters were located in the valid region and the experimental confirmation tests conducted showed good accordance between predicted and experimental values. Under these optimal conditions, the water absorption of the grafted modified glass fiber was improved from 13.6% to 23%; the tensile strength was enhanced and the peeling strength of the glass fiber reinforced PVDF composite membrane was improved by 23.7% and 32.6% with an AM concentration at 1 wt.% and 2 wt.%. The surface composition and microstructure of AM grafted glass fiber were studied via several techniques including Field Emission Scanning Electron Microscopy (FESEM), Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and energy dispersive X-ray spectroscopy (EDX). The analysis of the EDX and FTIR-ATR results confirmed that the AM was grafted to the glass fiber successfully by detecting and proving the existence of nitrogen atoms in the GFRP-CM. PMID:26899659

We present our research results on membranepores. The study was divided into two primary sections. The first involved the formation of protein pores in free-standing lipid bilayer membranes. The second involved the fabrication via surface micromachining techniques and subsequent testing of solid-state nanopores using the same characterization apparatus and procedures as that used for the protein pores. We were successful in our ability to form leak-free lipid bilayers, to detect the formation of single protein pores, and to monitor the translocation dynamics of individual homogeneous 100 base strands of DNA. Differences in translocation dynamics were observed when the base was switched from adenine to cytosine. The solid state pores (2-5 nm estimated) were fabricated in thin silicon nitride membranes. Testing of the solid sate pores indicated comparable currents for the same size protein pore with excellent noise and sensitivity. However, there were no conditions under which DNA translocation was observed. After considerable effort, we reached the unproven conclusion that multiple (<1 nm) pores were formed in the nitride membrane, thus explaining both the current sensitivity and the lack of DNA translocation blockages.

Using unbiased atomic-detailed molecular dynamics simulations, the C-terminal fragments of TDP-43 are observed to aggregate and form disordered-toroidal pores in a lipid bilayer. Cytotoxicity of TDP-43 may be inferred from the observation that the membranepores catalyze lipid flip-flop between bilayer leaflets and conduct water at high rates. PMID:27224887

To perform its barrier function, the lipid bilayer membrane requires a robust resistance against pore formation. Using a self-consistent field (SCF) theory and a molecularly detailed model for membranes composed of charged or zwitterionic lipids, it is possible to predict structural, mechanical, and thermodynamical parameters for relevant lipid bilayer membranes. We argue that the edge energy in membranes is a function of the spontaneous lipid monolayer curvature, the mean bending modulus, and the membrane thickness. An analytical Helfrich-like model suggests that most bilayers should have a positive edge energy. This means that there is a natural resistance against pore formation. Edge energies evaluated explicitly in a two-gradient SCF model are consistent with this. Remarkably, the edge energy can become negative for phosphatidylglycerol (e.g., dioleoylphosphoglycerol) bilayers at a sufficiently low ionic strength. Such bilayers become unstable against the formation of pores or the formation of lipid disks. In the weakly curved limit, we study the curvature dependence of the edge energy and evaluate the preferred edge curvature and the edge bending modulus. The latter is always positive, and the former increases with increasing ionic strength. These results point to a small window of ionic strengths for which stable pores can form as too low ionic strengths give rise to lipid disks. Higher order curvature terms are necessary to accurately predict relevant pore sizes in bilayers. The electric double layer overlap across a small pore widens the window of ionic strengths for which pores are stable.

Novel pore-filled polyelectrolyte membrane (PEM) was produced using track etched polycarbonate (PC) as porous substrate and poly(vinyl alcohol) (PVA) as pore filling material. PVA in PC pores was stabilized through cross-linking of PVA matrix with glutaraldehyde (GA). Cross-link time was varied from 24 h to 96 h while keeping the membranes in GA solution. Pore sizes of substrate PC membrane tested were 0.01, 0.1 and 0.2 μm. The membranes were characterized by Fourier-transform infrared spectroscopy and scanning electron microscopy. Ionic conductivity, water uptake, contact angle and gel content have been measured to determine membranes performance. The ionic crossover (iron ions and protons) through membranes was studied in a complete fuel cell. The single-cell performance of membrane was tested in a cathodic microbial fuel cell (MFC, Biogenerator). The physiochemical properties and membranes fuel cell performance were highly depended on the cross-link density of PVA matrices. Membranes cross-liked with GA for 72 h showed maximum gel content and their peak power density has reached 110 mW cm-2 at current density of 378 mA cm-2. Among all, membrane cross-linked for 72 h was studied for continuous long-term stability, which showed consistency for application in MFC.

We explore the effects of the peripheral and transmembrane antimicrobial peptides on the lipid bilayer membrane by using the coarse grained Dissipative Particle Dynamics simulations. We study peptide/lipid membrane complexes by considering peptides with various structure, hydrophobicity and peptide/lipid interaction strength. The role of lipid/water interaction is also discussed. We discuss a rich variety of membrane morphological changes induced by peptides, such as pore formation, membrane corrugation and Euler buckling. PMID:23579956

Bax protein plays a key role in mitochondrial membrane permeabilization and cytochrome c release upon apoptosis. Our recent data have indicated that the 20-residue C-terminal peptide of Bax (BaxC-KK; VTIFVAGVL-TASLTIWKKMG), when expressed intracellularly, translocates to the mitochondria and exerts lethal effect on cancer cells. Moreover, the BaxC-KK peptide, as well as two mutants where the two lysines are replaced with glutamate (BaxC-EE) or leucine (BaxC-LL), have been shown to form relatively large pores in lipid membranes, composed of up to eight peptide molecules per pore. Here the pore structure is analyzed by polarized Fourier transform infrared, circular dichroism, and fluorescence experiments on the peptides reconstituted in phospholipid membranes. The peptides assume an α/β-type secondary structure within membranes. Both β-strands and α-helices are significantly (by 30–60 deg) tilted relative to the membrane normal. The tryptophan residue embeds into zwitterionic membranes at 8–9 Å from the membrane center. The membrane anionic charge causes a deeper insertion of tryptophan for BaxC-KK and BaxC-LL but not for BaxC-EE. Combined with the pore stoichiometry determined earlier, these structural constraints allow construction of a model of the pore where eight peptide molecules form an “α/β-ring” structure within the membrane. These results identify a strong membranotropic activity of Bax C-terminus and propose a new mechanism by which peptides can efficiently perforate cell membranes. Knowledge on the pore forming mechanism of the peptide may facilitate development of peptide-based therapies to kill cancer or other detrimental cells such as bacteria or fungi. PMID:23110300

Nuclear pore complexes in the nuclear membrane act as the sole gateway of transport of molecules from the cytoplasm to the nucleus and vice versa. Studies on biomolecular transport through nuclear membranes provide vital data on the nuclear pore complexes. In this work, we use fluorescein isothiocyanate-labeled dextran molecules as a model system and study the passive nuclear import of biomolecules through nuclear pore complexes in digitonin-permeabilized HeLa cells. Experiments are carried out under transient conditions in the time lapse imaging scheme using an in-house constructed confocal laser scanning microscope. Transport rates of dextran molecules having molecular weights of 4-70 kDa corresponding to Stokes radius of 1.4-6 nm are determined. Analyzing the permeability of the nuclear membrane for different sizes the effective pore radius of HeLa cell nuclear membrane is determined to be 5.3 nm, much larger than the value reported earlier using proteins as probe molecules. The range of values reported for the nuclear pore radius suggest that they may not be rigid structures and it is quite probable that the effective pore size of nuclear pore complexes is critically dependent on the probe molecules and on the environmental factors. PMID:27338984

The membrane attack complex and perforin proteins (MACPFs) and bacterial cholesterol-dependent cytolysins (CDCs) are two branches of a large and diverse superfamily of pore-forming proteins that function in immunity and pathogenesis. During pore formation, soluble monomers assemble into large transmembrane pores through conformational transitions that involve extrusion and refolding of two α-helical regions into transmembrane β-hairpins. These transitions entail a dramatic refolding of the protein structure, and the resulting assemblies create large holes in cellular membranes, but they do not use any external source of energy. Structures of the membrane-bound assemblies are required to mechanistically understand and modulate these processes. In this Commentary, we discuss recent advances in the understanding of assembly mechanisms and molecular details of the conformational changes that occur during MACPF and CDC pore formation. PMID:27179071

Effector translocation is central to the virulence of many bacterial pathogens, including Streptococcus pyogenes, which utilizes the cholesterol-dependent cytolysin Streptolysin O (SLO) to translocate the NAD(+) glycohydrolase SPN into host cells during infection. SLO's translocation activity does not require host cell membrane cholesterol or pore formation by SLO, yet SLO does form pores during infection via a cholesterol-dependent mechanism. Although cholesterol was considered the primary receptor for SLO, SLO's membrane-binding domain also encodes a putative carbohydrate-binding site, implicating a potential glycan receptor in binding and pore formation. Analysis of carbohydrate-binding site SLO mutants and carbohydrate-defective cell lines revealed that glycan recognition is involved in SLO's pore formation pathway and is an essential step when SLO is secreted by non-adherent bacteria, as occurs during lysis of erythrocytes. However, SLO also recognizes host cell membranes via a second mechanism when secreted from adherent bacteria, which requires co-secretion of SPN but not glycan binding by SLO. This SPN-mediated membrane binding of SLO correlates with SPN translocation, and requires SPN's non-enzymatic domain, which is predicted to adopt the structure of a carbohydrate-binding module. SPN-dependent membrane binding also promotes pore formation by SLO, demonstrating that pore formation can occur by distinct pathways during infection. PMID:26059530

Pore-forming toxins (PFTs) are proteins that are secreted as soluble molecules and are inserted into membranes to form oligomeric transmembrane pores. In this paper, we report the crystal structure of Fragaceatoxin C (FraC), a PFT isolated from the sea anemone Actinia fragacea, at 1.8 Å resolution. It consists of a crown-shaped nonamer with an external diameter of about 11.0 nm and an internal diameter of approximately 5.0 nm. Cryoelectron microscopy studies of FraC in lipid bilayers reveal the pore structure that traverses the membrane. The shape and dimensions of the crystallographic oligomer are fully consistent with the membranepore. The FraC structure provides insight into the interactions governing the assembly process and suggests the structural changes that allow for membrane insertion. We propose a nonameric pore model that spans the membrane by forming a lipid-free α-helical bundle pore. PMID:21300287

Nanoporous anodic aluminum oxide (AAO) tubular membranes were fabricated from aluminum alloy tubes in sulfuric and oxalic acid electrolytes using a two-step anodization process. The membranes were investigated for characteristics such as pore size, interpore distance and thickness by varying applied voltage and electrolyte concentration. Morphology of the membranes was examined using light optical and scanning electron microscopy and characterized using ImageJ software. Results showed that membranes having narrow pore size and uniform pore distribution with parallel channel arrays were obtained. The pore sizes were ranging from 14 to 24 nm and the wall thicknesses as high as 76 microm. It was found that the pore size increased in direct proportion with the applied voltage and inversely with the electrolyte concentration while the interpore distance increased linearly with the applied voltage. It was also observed that increase in acid concentration increased tubular membrane wall thickness that improved mechanical handling. By using anodic alumina technology, robust ceramic tubes with uniformly distributed pore-structure and parallel nano-channels of lengths and sizes practical for industrial applications were reliably produced in quantity. PMID:19578471

Nanoporous anodic aluminum oxide (AAO) tubular membranes were fabricated from aluminum alloy tubes in sulfuric and oxalic acid electrolytes using a two-step anodization process. The membranes were investigated for characteristics such as pore size, interpore distance and thickness by varying applied voltage and electrolyte concentration. Morphology of the membranes was examined using light optical and scanning electron microscopy and characterized using ImageJ software. Results showed that membranes having narrow pore size and uniform pore distribution with parallel channel arrays were obtained. The pore sizes were ranging from 14 to 24 nm and the wall thicknesses as high as 76 µm. It was found that the pore size increased in direct proportion with the applied voltage and inversely with the electrolyte concentration while the interpore distance increased linearly with the applied voltage. It was also observed that increase in acid concentration increased tubular membrane wall thickness that improved mechanical handling. By using anodic alumina technology, robust ceramic tubes with uniformly distributed pore-structure and parallel nano-channels of lengths and sizes practical for industrial applications were reliably produced in quantity. PMID:19578471

Regulated exocytosis is a process that strongly depends on the formation and stability of the fusion pore. It was indicated experimentally and theoretically that narrow and highly curved fusion pore may be stabilized by accumulation of anisotropic membrane components possessing orientational ordering. On the other hand, narrow fusion pore may also undergo repetitive opening and closing, disruption in the so called kiss and run process or become completely opened in the process of full fusion of the vesicle with the membrane. In this paper we attempt to elucidate the subtle interplay between the stabilizing and destabilizing processes in the fusion neck. A possible physical mechanism which may lead to disruption of the stable fusion pore or complete fusion of the vesicle with the membrane is discussed. It is indicated that topologically driven defects of the in-plane orientational membrane ordering in the region of the fusion pore may disrupt the fusion. Alternatively, it may facilitate repetitive opening and closing of the fusion pore or induce full fusion of the vesicle with the target membrane. PMID:22541648

Tension plays a vital role in pore formation in biomembranes, but the mechanism of pore formation remains unclear. We investigated the temperature dependence of the rate constant of constant tension (σ)-induced pore formation in giant unilamellar vesicles of lipid membranes using an experimental method we developed. By analyzing this result, we determined the activation energy (Ua) of tension-induced pore formation as a function of tension. A constant (U0) that does not depend on tension was found to contribute significantly to Ua. Analysis of the activation energy clearly indicated that the dependence of Ua on σ in the classical theory is correct, but that the classical theory of pore formation is not entirely correct due to the presence of U0. We can reasonably consider that U0 is a nucleation free energy to form a hydrophilic pre-pore from a hydrophobic pre-pore or a region with lower lateral lipid density. After obtaining U0, the evolution of a pre-pore follows a classical theory. Our data provide valuable information that help explain the mechanism of tension-induced pore formation in biomembranes and lipid membranes.

Nonenveloped viruses are generally released from the cell by the timely lysis of host cell membranes. SV40 has been used as a model virus for the study of the lytic nonenveloped virus life cycle. The expression of SV40 VP4 at later times during infection is concomitant with cell lysis. To investigate the role of VP4 in viral release and its mechanism of action, VP4 was expressed and purified from bacteria as a fusion protein for use in membrane disruption assays. Purified VP4 perforated membranes as demonstrated by the release of fluorescent markers encapsulated within large unilamellar vesicles or liposomes. Dynamic light scattering results revealed that VP4 treatment did not cause membrane lysis or change the size of the liposomes. Liposomes encapsulated with 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-3-indacene-labeled streptavidin were used to show that VP4 formed stable pores in membranes. These VP4 pores had an inner diameter of 1-5 nm. Asymmetrical liposomes containing pyrene-labeled lipids in the outer monolayer were employed to monitor transbilayer lipid diffusion. Consistent with VP4 forming toroidal pore structures in membranes, VP4 induced transbilayer lipid diffusion or lipid flip-flop. Altogether, these studies support a central role for VP4 acting as a viroporin in the disruption of cellular membranes to trigger SV40 viral release by forming toroidal pores that unite the outer and inner leaflets of membrane bilayers. PMID:23651212

Pore-forming toxins have evolved to induce membrane injury by formation of pores in the target cell that alter ion homeostasis and lead to cell death. Many pore-forming toxins use cholesterol, sphingolipids, or other raft components as receptors. However, the role of plasma membrane organization for toxin action is not well understood. In this study, we have investigated cellular dynamics during the attack of equinatoxin II, a pore-forming toxin from the sea anemone Actinia equina, by combining time lapse three-dimensional live cell imaging, fluorescence recovery after photobleaching, FRET, and fluorescence cross-correlation spectroscopy. Our results show that membrane binding by equinatoxin II is accompanied by extensive plasma membrane reorganization into microscopic domains that resemble coalesced lipid rafts. Pore formation by the toxin induces Ca2+ entry into the cytosol, which is accompanied by hydrolysis of phosphatidylinositol 4,5-bisphosphate, plasma membrane blebbing, actin cytoskeleton reorganization, and inhibition of endocytosis. We propose that plasma membrane reorganization into stabilized raft domains is part of the killing strategy of equinatoxin II. PMID:21885440

Polymeric membranes are widely used in aeration systems for biological treatment. These membranes may degrade over time and are sensitive to fouling and scaling. Membrane degradation is reflected in a decline in operating performance and higher headloss, resulting in increased energy costs. Mechanical property parameters, such as membrane hardness, Young's modulus, and orifice creep, were used to characterize the performance of membranes over time in operation and to predict their failure. Used diffusers from municipal wastewater treatment plants were collected and tested for efficiency and headloss, and then dissected to facilitate measurements of Young's modulus, hardness, and orifice creep. Higher degree of membrane fouling corresponded consistently with larger orifice creep. A lab-scale membrane ageing simulation was performed with polyurethane and four different ethylene-propylene-diene (EPDM) membrane diffusers by subjecting them to chemical ageing cycles and periodic testing. The results confirmed full-scale plant results and showed the superiority of orifice creep over Young's modulus and hardness in predicting diffuser deterioration. PMID:17706264

Granules isolated from CTL and NK cells contain a cytolytic pore-forming protein (PFP/perforin). At low temperatures (on ice), PFP binds to erythrocyte membranes without producing hemolysis. Hemolysis occurs when the PFP-bound erythrocytes are warmed up to 37 degrees C, which defines a temperature-dependent, lytic (pore-formation) step distinct from the membrane-binding event. Ca2+ and neutral pH are required for both membrane binding and pore formation by PFP. Serum, LDL, HDL, and heparin inhibit the hemolytic activity of PFP by blocking its binding to lipid membranes. Lysis by PFP that has bound to erythrocyte membranes is no longer susceptible to the effect of these inhibitors. The hemolytic activities associated with intact granules and solubilized PFP show different requirements for Ca2+ and pH, indicating that cytolysis produced by isolated granules may involve an additional step, possibly fusion of granules with membranes. It is suggested that three distinct Ca2+- and pH-dependent events may be involved during cell killing by CTL and NK cells: fusion of cytoplasmic granules of effector cells with their plasma membrane, releasing PFP from cells; binding of the released PFP to target membranes; and insertion of monomers and the subsequent formation of lytic pores in the target membrane. The serum-mediated inhibition of membrane binding by PFP could prevent the accidental injury of bystander cells by cell-released PFP, but would allow cytolysis to proceed to completion once PFP has bound to the target membrane. PMID:3494808

Membrane attack complex/perforin/cholesterol-dependent cytolysin (MACPF/CDC) proteins constitute a major superfamily of pore-forming proteins that act as bacterial virulence factors and effectors in immune defence. Upon binding to the membrane, they convert from the soluble monomeric form to oligomeric, membrane-inserted pores. Using real-time atomic force microscopy (AFM), electron microscopy (EM), and atomic structure fitting, we have mapped the structure and assembly pathways of a bacterial CDC in unprecedented detail and accuracy, focussing on suilysin from Streptococcus suis. We show that suilysin assembly is a noncooperative process that is terminated before the protein inserts into the membrane. The resulting ring-shaped pores and kinetically trapped arc-shaped assemblies are all seen to perforate the membrane, as also visible by the ejection of its lipids. Membrane insertion requires a concerted conformational change of the monomeric subunits, with a marked expansion in pore diameter due to large changes in subunit structure and packing. DOI: http://dx.doi.org/10.7554/eLife.04247.001 PMID:25457051

How antimicrobial peptides form pores in membranes is of interest as a fundamental membrane process. However, the underlying molecular mechanism, which has potential applications in therapeutics, nonviral gene transfer, and drug delivery, has been in dispute. We have resolved this mechanism by observing the time-dependent process of pore formation in individual giant unilamellar vesicles (GUVs) exposed to a melittin solution. An individual GUV first expanded its surface area at constant volume and then suddenly reversed to expanding its volume at constant area. The area expansion, the volume expansion, and the point of reversal all match the results of equilibrium measurements performed on peptide–lipid mixtures. The mechanism includes a negative feedback that makes peptide-induced pores stable with a well defined size, contrary to the suggestion that peptides disintegrate the membrane in a detergent-like manner. PMID:18375755

A porous membrane filter is one of the key components for sample preparation in lab-on-a-chip applications. However, most of the membranes reported to date have only been used for size-based separation since it is difficult to provide functionality to the membrane or improve the performance of the membrane. In this work, as a method to functionalize the membrane filter, controlling the shape of the membranepores is suggested, and a convenient and mass-producible fabrication method is provided. With the proposed method, membrane filters with round, conical and funnel shape pores were successfully fabricated, and we demonstrated that the sidewall slope of the conical shape pores could be precisely controlled. To verify that the membrane filter can be functionalized by controlled pore shape, we investigated filtration and trapping performance of the membrane filter with conical shape pores. In a filtration test of 1000 cancer cells (MCF-7, a breast cancer cell line) spiked in phosphate buffered saline (PBS) solution, 77% of the total cancer cells were retained on the membrane, and each cell from among 99.3% of the retained cells was automatically isolated in a single conical pore during the filtration process. Thanks to its engineered pore shape, trapping ability of the membrane with conical pores is dramatically improved. Microparticles trapped in the conical pores maintain their locations without any losses even at a more than 30 times faster external flow rate com-pared with those mounted on conventional cylindrical pores. Also, 78% of the cells trapped in the conical pores withstand an external flow of over 300 μl min-1 whereas only 18% of the cells trapped in the cylindrical pores remain on the membrane after 120 μl min-1 of an external flow is applied.

Summary As a cellular organelle, the cilium contains a unique protein composition [1, 2]. Entry of both membrane [3–5] and cytosolic components [6–8] is tightly regulated by gating mechanisms at the cilium base, however, the mechanistic details of ciliary gating are largely unknown. We previously proposed that entry of cytosolic components is regulated by mechanisms similar to those of nuclear transport and is dependent on nucleoporins (NUPs) which comprise a ciliary pore complex (CPC) [6, 9]. To investigate ciliary gating mechanisms, we developed a system to clog the pore by inhibiting NUP function via forced dimerization. We targeted NUP62, a component of the central channel of the nuclear pore complex (NPC) [10], for forced dimerization by tagging it with the homodimerizing Fv domain. As proof of principle, we show that forced dimerization of NUP62-Fv attenuated active transport of bovine serum albumin into the nuclear compartment and of the kinesin-2 motor KIF17 into the ciliary compartment. Using the pore clogging technique, we find that forced dimerization of NUP62 attenuated the gated entry of cytosolic proteins but did not affect entry of membrane proteins or diffusional entry of small cytosolic proteins. We propose a model in which active transport of cytosolic proteins into both nuclear and ciliary compartments requires functional NUPs of the central pore whereas lateral entry of membrane proteins utilizes a different mechanism that is likely specific to each organelle’s limiting membrane. PMID:25264252

Self-supporting membranes containing either isolated or organized arrays of nanosized pores have been prepared using a nonlithographic approach by coupling sol-gel processing, thin film preparation, and templating. Specifically, polystyrene latex spheres were doped into a hybrid sol prepared from tetraethoxysilane and dimethyldiethoxysilane and the resultant sol spin cast on a sacrificial support. Upon removal of the template and the sacrificial support, the self-supporting nanopore membranes were transferred to glass for characterization by atomic force microscopy and scanning electron microscopy. Through variations in the thickness of the membranes and the size of the polystyrene latex spheres, the geometry (cylinder-like to asymmetric-like) and the dimensions of the nanopores were altered. Pores with diameters that range from 35 to 2100 nm, aspect ratios (defined as the top pore diameter divided by the bottom pore diameter) from 1-4, and depths (effective film thickness) from 50 to 1500 nms have been prepared using templates that range in diameter from 100 to 3100 nm. The method described employs "wet-chemistry", is highly versatile, and is easily amenable to modification by utilizing templates of different sizes and geometries to create stable membranes with different pore geometries and sizes that can be used as platforms for nanofiltration and/or chemical sensors. PMID:19206497

A new reaction coordinate to bias molecular dynamics simulation is described that allows enhanced sampling of density-driven processes, such as mixing and demixing two different molecular species. The methodology is validated by comparing the theoretical entropy of demixing two ideal gas species and then applied to induce deformation and pore formation in phospholipid membranes within an umbrella sampling framework. Comparison with previous biased simulations of membranepore formation suggests overall quantitative agreement, but the density-based biasing potential results in a different, more realistic transition pathway than that in previous studies. PMID:25620896

Improved hybrid polymer electrolyte membranes are introduced based on ether-modified polysiloxanes and poly(vinylidene fluoride-co-hexafluoropropylene) yielding a safe separator membrane, which is able to be sprayed directly onto lithium ion battery active materials, with an active role for enhanced ion transport. PMID:26121633

PVDF-g-PAN has been synthesized by grafting polyacrylonitrile onto polyvinylidene fluoride using an ATRP/AGET method. The novel polymer is ionically conducive and has much more flexibility than PVDF alone, making it especially useful either as a binder in battery cell electrodes or as a polymer electrolyte in a battery cell.

Parkinson’s disease (PD) and Dementia with Lewy bodies are common disorders of the aging population characterized by the progressive accumulation of α-synuclein (α-syn) in the CNS. Aggregation of α-syn into oligomers with a ring-like appearance has been proposed a role in toxicity. However, the molecular mechanisms and the potential sequence of events involved in the formation of pore-like structures are unclear. We utilized computer modeling and cell-based studies to investigate the process of α-syn (wild type and A53T) oligomerization in membranes. The studies suggest that α-syn rapidly penetrates the membrane, changing its conformation from α-helical toward a coiled structure. This penetration facilitate the incorporation of additional α-syn monomers to the complex, and subsequent displacement of phospholipids, and formation of oligomers in the membrane. This process occurred more rapidly, and with more favorable energy of interaction for mutant A53T compared with wild type α-syn. After 4 ns of simulation for the protein-membrane model α-syn penetrated through two thirds of the membrane. By 9 ns, the penetration of the annular α-syn oligomers can result in the formation of pore-like structures that fully perforate the lipid bilayer. Experimental incubation of recombinant α-syn in synthetic membranes resulted in the formation of similar pore-like complexes. Moreover, mutant (A53T) α-syn had a greater tendency to accumulate in neuronal membrane fractions in cell cultures, resulting in greater neuronal permeability with the calcein efflux assay. These studies provide a sequential molecular explanation for the process of α-syn oligomerization in the membrane, and support the role of formation of pore-like structures in the pathogenesis of the neurodegenerative process in PD. PMID:22251432

Fundamental understanding of the ion transport in membrane systems by diffusion, electromigration and advection is important in widespread processes such as de-ionization by reverse osmosis and electrodialysis and electro-osmotic micropumps. Here we revisit the classical analysis of a single cylindrical pore, see e.g. Gross and Osterle [J Chem Phys 49, 228 (1968)]. We extend the analysis by including the well-established concept of contacting stagnant diffusion layers on either side of the pore; thus, the pore is not in direct equilibrium with the reservoirs. Inside the pore the ions are assumed to be in quasi-equilibrium in the radial direction with the surface charge on the pore wall and we obtain a 1D model by area-averaging. We demonstrate that in some extreme limits this model reduces to simpler models studied in the literature; see e.g. Yaroshchuk [J Membrane Sci 396, 43 (2012)]. Using our model we present predictions of important transport effects such as variation of transport numbers inside the membrane, onset of limiting current, and transient dynamics described by the method of characteristics.

Summary Human body surface epithelia coexist in close association with complex bacterial communities and are protected by a variety of antibacterial proteins. C-type lectins of the RegIII family are bactericidal proteins that limit direct contact between bacteria and the intestinal epithelium and thus promote tolerance to the intestinal microbiota1,2. RegIII lectins recognize their bacterial targets by binding peptidoglycan carbohydrate1,3 but the mechanism by which they kill bacteria is unknown. Here we elucidate the mechanistic basis for RegIII bactericidal activity. Here we show that human RegIIIα (hRegIIIα, also known as HIP/PAP) binds membrane phospholipids and kills bacteria by forming a hexameric membrane-permeabilizing oligomeric pore. We derive a three-dimensional model of the hRegIIIα pore by docking the hRegIIIα crystal structure into a cryo-electron microscopic map of the pore complex, and show that the model accords with experimentally determined properties of the pore. Lipopolysaccharide inhibits hRegIIIα pore-forming activity, explaining why hRegIIIα is bactericidal for Gram-positive but not Gram-negative bacteria. Our findings identify C-type lectins as mediators of membrane attack in the mucosal immune system, and provide detailed insight into an antibacterial mechanism that promotes mutualism with the resident microbiota. PMID:24256734

We investigated the effect of charge on the membrane morphology of giant unilamellar vesicles (GUVs) composed of various mixtures containing charged lipids. We observed the membrane morphologies by fluorescent and confocal laser microscopy in lipid mixtures consisting of a neutral unsaturated lipid [dioleoylphosphatidylcholine (DOPC)], a neutral saturated lipid [dipalmitoylphosphatidylcholine (DPPC)], a charged unsaturated lipid [dioleoylphosphatidylglycerol (DOP G(-)) ], a charged saturated lipid [dipalmitoylphosphatidylglycerol (DPP G(-)) ], and cholesterol (Chol). In binary mixtures of neutral DOPC-DPPC and charged DOPC -DPP G(-) , spherical vesicles were formed. On the other hand, pore formation was often observed with GUVs consisting of DOP G(-) and DPPC. In a DPPC-DPPG(-) -Chol ternary mixture, pore-formed vesicles were also frequently observed. The percentage of pore-formed vesicles increased with the DPP G(-) concentration. Moreover, when the head group charges of charged lipids were screened by the addition of salt, pore-formed vesicles were suppressed in both the binary and ternary charged lipid mixtures. We discuss the mechanisms of pore formation in charged lipid mixtures and the relationship between phase separation and the membrane morphology. Finally, we reproduce the results seen in experimental systems by using coarse-grained molecular dynamics simulations.

The poly(acrylic acid)-graft-poly(vinylidene fluoride) (PAAc-g-PVDF) and poly(4-vinylpyridine)-graft-poly(vinylidene fluoride) (P4VP-g-PVDF) copolymers were obtained by thermally induced molecular graft copolymerization of acrylic acid (AAc) and 4-vinylpyridine (4VP), respectively, with the ozone-pretreated poly(vinylidene fluoride) (PVDF) in N-methyl-2-pyrrolidone (NMP) solution. Microfiltration (MF) membranes were prepared from the respective copolymers by phase inversion in aqueous media. The effects of pH of the coagulation bath on the physicochemical and morphological characteristics of the membranes were investigated. The surface compositions of the membranes were determined by X-ray photoelectron spectroscopy (XPS). The surface graft concentration of the AAc polymer for the PAAc-g-PVDF MF membrane increased with decreasing pH value of the coagulation bath. Completely opposite pH-dependent behavior was observed for the surface graft concentration of the 4VP polymer in the P4VP-g-PVDF MF membranes. A substantial increase in mean pore size was observed for the PAAc-g-PVDF MF membranes cast in basic coagulation baths of increasing pH. In the case of the P4VP-g-PVDF MF membranes, a substantial increase in mean pore size was observed for membranes cast in low pH (acidic) baths. The permeation rate of aqueous solutions through the PAAc-g-PVDF and P4VP-g-PVDF MF membranes exhibited a reversible dependence on the pH of the solution, with the membranes cast near the neutral pH exhibiting the highest sensitivity to changes in permeate pH. PMID:12962674

The size of pores formed in the plasma membrane by various substances is frequently determined using polyethylene glycols as osmotic protectants. In this work, we have found that the size of pores formed by saponin in the red blood cell membrane determined by hemolysis versus molecular weight of polyethylene glycol was different to that estimated by light dispersion of cell suspensions. After complete swelling of cells induced by saponin in semiisotonic salt media containing 150 mOsm PEG-4000 or PEG-3000, a significant increase in the light absorbance at 640 nm was developed resulting from the formation of hemoglobin precipitates. Easily sedimenting aggregates were also formed when the supernatant of lysed cells was added to the equiosmotic solutions of polyethylene glycols with molecular weight higher than 1000. We suggest that the real size of large pores could be underestimated due to the phenomenon of hemoglobin precipitation by polyethylene glycols. PMID:18692020

We address the possibility of being able to induce the trafficking of salt ions and other solutes across cell membranes without the use of specific protein-based transporters or pumps. On the basis of realistic atomic-scale molecular dynamics simulations, we demonstrate that transmembrane ionic leakage can be initiated by chemical means, in this instance through addition of dimethyl sulfoxide (DMSO), a solvent widely used in cell biology. Our results provide compelling evidence that the small amphiphilic solute DMSO is able to induce transient defects (water pores) in membranes and to promote a subsequent diffusive pore-mediated transport of salt ions. The findings are consistent with available experimental data and offer a molecular-level explanation for the experimentally observed activities of DMSO solvent as an efficient penetration enhancer and a cryoprotectant, as well as an analgesic. Our findings suggest that transient pore formation by chemical means could emerge as an important general principle for therapeutics. PMID:17983219

Small-diameter carbon nanotubes (CNTs) are shown to enable exceptionally fast transport of water vapor under a concentration gradient driving force. Thanks to this property, membranes having sub-5 nm CNTs as conductive pores feature outstanding breathability while maintaining a high degree of protection from biothreats by size exclusion. PMID:27159328

Here, small-diameter carbon nanotubes (CNTs) are shown to enable exceptionally fast transport of water vapor under a concentration gradient driving force. Thanks to this property, membranes having sub-5 nm CNTs as conductive pores feature outstanding breathability while maintaining a high degree of protection from biothreats by size exclusion.

ABSTRACT Intracellular killing of Streptococcus pneumoniae is complemented by induction of macrophage apoptosis. Here, we show that the toxin pneumolysin (PLY) contributes both to lysosomal/phagolysosomal membrane permeabilization (LMP), an upstream event programing susceptibility to apoptosis, and to apoptosis execution via a mitochondrial pathway, through distinct mechanisms. PLY is necessary but not sufficient for the maximal induction of LMP and apoptosis. PLY’s ability to induce both LMP and apoptosis is independent of its ability to form cytolytic pores and requires only the first three domains of PLY. LMP involves TLR (Toll-like receptor) but not NLRP3/ASC (nucleotide-binding oligomerization domain [Nod]-like receptor family, pyrin domain-containing protein 3/apoptosis-associated speck-like protein containing a caspase recruitment domain) signaling and is part of a PLY-dependent but phagocytosis-independent host response that includes the production of cytokines, including interleukin-1 beta (IL-1β). LMP involves progressive and selective permeability to 40-kDa but not to 250-kDa fluorescein isothiocyanate (FITC)-labeled dextran, as PLY accumulates in the cytoplasm. In contrast, the PLY-dependent execution of apoptosis requires phagocytosis and is part of a host response to intracellular bacteria that also includes NO generation. In cells challenged with PLY-deficient bacteria, reconstitution of LMP using the lysomotrophic detergent LeuLeuOMe favored cell necrosis whereas PLY reconstituted apoptosis. The results suggest that PLY contributes to macrophage activation and cytokine production but also engages LMP. Following bacterial phagocytosis, PLY triggers apoptosis and prevents macrophage necrosis as a component of a broad-based antimicrobial strategy. This illustrates how a key virulence factor can become the focus of a multilayered and coordinated innate response by macrophages, optimizing pathogen clearance and limiting inflammation. PMID:25293758

ABSTRACT In naked viruses, membrane breaching is a key step that must be performed for genome transfer into the target cells. Despite its importance, the mechanisms behind this process remain poorly understood. The small protein VP4, encoded by the genomes of most viruses of the order Picornavirales, has been shown to be involved in membrane alterations. Here we analyzed the permeabilization activity of the natively nonmyristoylated VP4 protein from triatoma virus (TrV), a virus belonging to the Dicistroviridae family within the Picornavirales order. The VP4 protein was produced as a C-terminal maltose binding protein (MBP) fusion to achieve its successful expression. This recombinant VP4 protein is able to produce membrane permeabilization in model membranes in a membrane composition-dependent manner. The induced permeability was also influenced by the pH, being greater at higher pH values. We demonstrate that the permeabilization activity elicited by the protein occurs through discrete pores that are inserted on the membrane. Sizing experiments using fluorescent dextrans, cryo-electron microscopy imaging, and other, additional techniques showed that recombinant VP4 forms heterogeneous proteolipidic pores rather than common proteinaceous channels. These results suggest that the VP4 protein may be involved in the membrane alterations required for genome transfer or cell entry steps during dicistrovirus infection. IMPORTANCE During viral infection, viruses need to overcome the membrane barrier in order to enter the cell and replicate their genome. In nonenveloped viruses membrane fusion is not possible, and hence, other mechanisms are implemented. Among other proteins, like the capsid-forming proteins and the proteins required for viral replication, several viruses of the order Picornaviridae contain a small protein called VP4 that has been shown to be involved in membrane alterations. Here we show that the triatoma virus VP4 protein is able to produce membrane

Background: The induction of the mitochondrial membrane permeability transition (MMPT) pore has been implicated in the cascade of events involved in apoptosis (programmed cell death). Olax subscorpioidea is traditionally used for the treatment of several diseases and infection. However, its role on MMPT is not yet established. This study was aimed at evaluating the effects of varying concentrations of the methanol leaf extract of O. subscorpioidea (MEOS) on MMPT pore opening, mitochondrial adenosine triphosphatase (ATPase), and mitochondrial lipid peroxidation. Materials and Methods: Opening of the pore was spectrophotometrically assayed under succinate-energized conditions. Results: In the absence of triggering agent (calcium), MEOS induced MMPT pore opening by 350, 612, 827, 845% at 36, 60, 86 and 112 μg/ml, respectively. MEOS further induced MMPT pore opening in the presence of a triggering agent by 866, 905, 831, 840, 949% at 12, 36, 60, 86 and 112 μg/ml, respectively. The extract significantly induced mitochondrial membrane lipid peroxidation in all the concentration used. MEOS also significantly increased mitochondrial ATP hydrolysis by mitochondrial ATPase in all concentration of the extract used. Conclusion: It may be deduced from this results, that MEOS contains certain bioactive components that may find use in pathological conditions that require an enhanced rate of apoptosis. PMID:26109790

Maculatin 1.1 (Mac1) showed potent activity against Staphylococcus aureus with an MIC of 7 μM. The mode of action of Mac1 was investigated by combining assays with S. aureus cells and lipid vesicles mimicking their membrane composition. A change in Mac1 conformation was monitored by circular dichroism from random coil to ca. 70% α-helix structure in contact with vesicles. Electron micrographs of S. aureus incubated with Mac1 showed rough and rippled cell surfaces. An uptake of 65% of small (FD, 4 kDa [FD-4]) and 35% of large (RD, 40 kDa [RD-40]) fluorescent dextrans by S. aureus was observed by flow cytometry and indicate that Mac1 formed a pore of finite size. In model membranes with both dyes encapsulated together, the full release of FD-4 occurred, but only 40% of RD-40 was reached, supporting the flow cytometry results, and indicating a pore size between 1.4 and 4.5 nm. Finally, solid-state nuclear magnetic resonance showed formation of an isotropic phase signifying highly mobile lipids such as encountered in a toroidal pore structure. Overall, Mac1 is a promising antimicrobial peptide with the potent capacity to form pores in S. aureus membranes. PMID:23689707

Cells permeabilized by the bacterial pore-forming toxin streptolysin O (SLO) reseal their plasma membrane in a Ca2+-dependent manner. Resealing involves Ca2+-dependent exocytosis of lysosomes, release of acid sphingomyelinase and rapid formation of endosomes that carry the transmembrane pores into the cell. The intracellular fate of the toxin-carrying endocytic vesicles, however, is still unknown. Here, we show that SLO pores removed from the plasma membrane by endocytosis are sorted into the lumen of lysosomes, where they are degraded. SLO-permeabilized cells contain elevated numbers of total endosomes, which increase gradually in size while transitioning from endosomes with flat clathrin coats to large multivesicular bodies (MVBs). Under conditions that allow endocytosis and plasma membrane repair, SLO is rapidly ubiquitinated and gradually degraded, in a process sensitive to inhibitors of lysosomal hydrolysis but not of proteasomes. The endosomes induced by SLO permeabilization become increasingly acidified and promote SLO degradation under normal conditions, but not in cells silenced for expression of Vps24, an ESCRT-III complex component required for the release of intraluminal vesicles into MVBs. Thus, cells dispose of SLO transmembrane pores by ubiquitination/ESCRT-dependent sorting into the lumen of late endosomes/lysosomes. PMID:22212686

Ion track membranes (ITM) have attracted significant interest over the past two decades due to their numerous applications in physical, biological, chemical, biochemical and medical experimental works. A particular feature of ITM technology is the possibility to fabricate samples with a predetermined number of pores, including single-poremembranes. The present report describes a procedure that allowed for the production of multi-, oligo- and single-poremembranes using a continuous ion beam from an IC-100 cyclotron. The beam was scanned over a set of small diaphragms, from 17 to ∼1000 μm in diameter. Ions passed through the apertures and impinged two sandwiched polymer foils, with the total thickness close to the ion range in the polymer. The foils were pulled across the ion beam at a constant speed. The ratio between the transport speed and the scanning frequency determined the distance between irradiation spots. The beam intensity and the aperture diameters were adjusted such that either several, one or no ions passed through the diaphragms during one half-period of scanning. After irradiation, the lower foil was separated from the upper foil and was etched to obtain pores 6-8 μm in diameter. The pores were found using a color chemical reaction between two reagents placed on opposite sides of the foil. The located pores were further confirmed using SEM and optical microscopy. The numbers of tracks in the irradiation spots were consistent with the Poisson statistics. Samples with single or few tracks obtained in this way were employed to study fine phenomena in ion track nanopores.

Equinatoxin II (EqtII), a eukaryotic pore-forming toxin, lyses cell membranes through a mechanism involving the insertion of its N-terminal α-helix into the membrane. EqtII pore formation is dependent on sphingomyelin (SM), although cholesterol (Chol) and membrane microdomains have also been suggested to enhance its activity. We have investigated the mechanism of EqtII binding and insertion by using neutron reflection to determine the structures of EqtII-membrane assemblies in situ. EqtII has several different modes of binding to membranes depending on the lipid composition. In pure dimyristoyl-phosphatidylcholine (DMPC) membranes, EqtII interacts weakly and reversibly with the lipid head groups in an orientation approximately parallel to the membrane surface. The presence of sphingomyelin (SM) gives rise to a more upright orientation of EqtII, but Chol is required for insertion into the core of the membrane. Cooling the EqtII-lipid assembly below the lipid phase transition temperature leads to deep water penetration and a significant reduction in the extension of the protein outside the membrane, indicating that phase-separation plays a role in EqtII pore-formation. An inactive double-cysteine mutant of EqtII in which the α-helix is covalently tethered to the rest of the protein, interacts only reversibly with all the membranes. Releasing the α-helix in situ by reduction of the disulphide bridge, however, causes the mutant protein to penetrate in DMPC-SM-Chol membranes in a manner identical to that of the wild-type protein. Our results help clarify the early steps in pore formation by EqtII and highlight the valuable information on protein-membrane interactions available from neutron reflection measurements. PMID:26706098

Antimicrobial peptides serve as defense weapons against bacteria. They are secreted by organisms of plants and animals and have a wide variety in composition and structure. In this study, we theoretically explore the effects of the antimicrobial peptides on the lipid bilayer membrane by using analytic arguments and the coarse grained dissipative particle dynamics simulations. We study peptide/lipid membrane complexes by considering peptides with various structure, hydrophobicity and peptide/lipid interaction strength. The role of lipid/water interaction is also discussed. We discuss a rich variety of membrane morphological changes induced by peptides, such as pore formation, membrane corrugation and Euler buckling. Such buckled membrane states have been indeed seen in a number of experiments with bacteria affected by peptide, yet this is the first theoretical study addressing these phenomena more deeply.

Pore structure in cellulose acetate ultrafiltration (UF) and reverse-osmosis (RO) membranes has been studied using small-angle neutron scattering. Scattering experiments were carried out on dry membranes as well as on membranes swollen with deuterated solvents (D[sub 2]O and CD[sub 3]OD). In addition, the RO membranes were studied both before and after annealing (a process of heating a membrane in a water bath at [approximately]75 C to improve its separation properties). The pore surface in UF membranes was found to be smooth and nonfractal, as evidenced by the fourth power law behavior at high Q. Values of average pore sizes obtained for dry and solvent swollen membranes agree well with pore sizes obtained by other methods. For cellulose acetate RO membranes in their dry state, the unannealed membrane appears to consist of two discrete pore size distributions in the intermediate and high Q region while the annealed membrane contains a much wider distribution of pore sizes. These results give a good account of the changes occurring in the structure of RO membranes as a result of annealing, and agree well with the prediction of other authors.

Whether an individual pore in a porous membrane can be imaged using scanning electrochemical microscopy (SECM), operated in ac impedance mode, is determined by the magnitude of the change in the total impedance of the imaging system as the SECM tip is scanned over the pore. In instances when the SECM tip resistance is small relative to the internal pore resistance, the total impedance changes by a negligible amount, rendering the pore invisible during impedance imaging. A simple solution to this problem is to introduce a low-impedance electrical shunt (i.e., a salt bridge) across the membrane. This principle is demonstrated by imaging polycarbonate membranes (6-12-microm thickness) containing between 1 and 2000 conical-shaped pores (60-nm- and 2.5-microm-diameter openings) using an approximately 1-microm-radius Pt tip. Theory and experiments show that image contrast (the change in ac current measured as the probe is scanned over the pore) is inversely proportional to the total resistance of the membrane and can be increased by a factor of approximately 50x by introducing a low-resistance electrical shunt across the membrane. Remarkably, SECM images of membranes containing a single high-resistance (approximately 1 G Omega) pore can only be imaged by short-circuiting the membrane. Image contrast also becomes independent of membrane resistance when an electrical shunt is used, allowing for more quantitative comparisons of the features in ac impedance images of different membranes. PMID:16970331

Defensins are cationic and disulfide-bonded host defense proteins of many animals that target microbial cell membranes. Elucidating the three-dimensional structure, dynamics and topology of these proteins in phospholipid bilayers is important for understanding their mechanisms of action. Using solid-state NMR spectroscopy, we have now determined the conformation, dynamics, oligomeric state and topology of a human α-defensin, HNP-1, in DMPC/DMPG bilayers. 2D correlation spectra show that membrane-bound HNP-1 exhibits a similar conformation to the water-soluble state, except for the turn connecting the β2 and β3 strands, whose sidechains exhibit immobilization and conformational perturbation upon membrane binding. At high protein/lipid ratios, rapid 1H spin diffusion from the lipid chains to the protein was observed, indicating that HNP-1 was well inserted into the hydrocarbon core of the bilayer. Arg Cζ-lipid 31P distances indicate that only one of the four Arg residues forms tight hydrogen-bonded guanidinium-phosphate complexes. The protein is predominantly dimerized at high protein/lipid molar ratios, as shown by 19F spin diffusion experiments. The presence of a small fraction of monomers and the shallower insertion at lower protein concentrations suggest that HNP-1 adopts concentration-dependent oligomerization and membrane-bound structure. These data strongly support a “dimer pore” topology of HNP-1 in which the polar top of the dimer lines an aqueous pore while the hydrophobic bottom faces the lipid chains. In this structure R25 lies closest to the membrane surface among the four Arg residues. The pore does not have large lipid disorder, in contrast to the toroidal pores formed by protegrin-1, a two-stranded β-hairpin antimicrobial peptide. These results provide the first glimpse into the membrane-bound structure and mechanism of action of human α-defensins. PMID:20961099

Abstract Cell-penetrating peptides like the cationic human immunodeficiency virus-1 trans-acting activator of transcription (TAT) peptide have the capability to traverse cell membranes and to deliver large molecular cargoes into the cellular interior. We used optical sectioning and state-of-the-art single-molecule microscopy to examine the passive membrane permeation of fluorescently labeled TAT peptides across the membranes of giant unilamellar vesicles (GUVs). In GUVs formed by phosphatidylcholine and cholesterol only, no translocation of TAT up to a concentration of 2 μM into the GUVs could be observed. At the same peptide concentration, but with 40 mol % of anionic phosphatidylserine in the membrane, rapid translocation of TAT peptides across the bilayers was detected. Efficient translocation of TAT peptides was observed across GUVs containing 20 mol % of phosphatidylethanolamine, which is known to induce a negative curvature into membranes. We discovered that TAT peptides are not only capable of penetrating membranes directly in a passive manner, but they were also able to form physical pores with sizes in the nanometer range, which could be passed by small dye tracer molecules. Lipid topology and anionic charge of the lipid bilayer are decisive parameters for pore formation. PMID:20655843

We study the indentation of a free-standing lipid membrane suspended over a nanopore on a hydrophobic substrate by means of molecular dynamics simulations. We find that in the course of indentation the membrane bends at the point of contact and the fringes of the membrane glide downward intermittently along the pore edges and stop gliding when the fringes reach the edge bottoms. The bending continues afterward, and the large strain eventually induces a phase transition in the membrane, transformed from a bilayered structure to an interdigitated structure. The membrane is finally ruptured when the indentation goes deep enough. Several local physical quantities in the pore regions are calculated, which include the tilt angle of lipid molecules, the nematic order, the included angle, and the distance between neighboring lipids. The variations of these quantities reveal many detailed, not-yet-specified local structural transitions of lipid molecules under indentation. The force-indentation curve is also studied and discussed. The results make a connection between the microscopic structure and the macroscopic properties and provide deep insight into the understanding of the stability of a lipid membrane spanning over nanopore. PMID:21859109

We find that curvature-driven growth of pores in electrically charged membranes correctly reproduces charge-pulse experiments. Our model, consisting of a Langevin equation for the time dependence of the pore radius coupled to an ordinary differential equation for the number of pores, captures the statistics of the pore population and its effect on the membrane conductance. The calculated pore radius is a linear, and not an exponential, function of time, as observed experimentally. Two other important features of charge-pulse experiments are recovered: pores reseal for low and high voltages but grow irreversibly for intermediate values of the voltage. Our set of coupled ordinary differential equations is equivalent to the partial differential equation used previously to study pore dynamics, but permits the study of longer timescales necessary for the simulations of voltage-clamp experiments. An effective phase diagram for such experiments is obtained. PMID:19186129

We find that curvature-driven growth of pores in electrically charged membranes correctly reproduces charge-pulse experiments. Our model, consisting of a Langevin equation for the time dependence of the pore radius coupled to an ordinary differential equation for the number of pores, captures the statistics of the pore population and its effect on the membrane conductance. The calculated pore radius is a linear, and not an exponential, function of time, as observed experimentally. Two other important features of charge-pulse experiments are recovered: pores reseal for low and high voltages but grow irreversibly for intermediate values of the voltage. Our set of coupled ordinary differential equations is equivalent to the partial differential equation used previously to study pore dynamics, but permits the study of longer timescales necessary for the simulations of voltage-clamp experiments. An effective phase diagram for such experiments is obtained. PMID:19186129

Membrane rafts are transient and unstable membrane microdomains that are enriched in sphingolipids, cholesterol, and specific proteins. They are involved in intracellular trafficking, signal transduction, pathogen entry, and attachment of various ligands. Increasing experimental evidence on the crucial biological roles of membrane rafts under normal and pathological conditions require new techniques for their structural and functional characterization. In particular, fluorescence-labeled cytolytic proteins that interact specifically with molecules enriched in rafts are of increasing interest. Cholera toxin subunit B interacts specifically with raft-residing ganglioside G(M1), and it has long been the lipid probe of choice for membrane rafts. Recently, four new pore-forming toxins have been proposed as selective raft markers: (i) equinatoxin II, a cytolysin from the sea anemone Actinia equina, which specifically recognizes free and membrane-embedded sphingomyelin; (ii) a truncated non-toxic mutant of a cytolytic protein, lysenin, from the earthworm Eisenia foetida, which specifically recognizes sphingomyelin-enriched membrane domains; (iii) a non-toxic derivative of the cholesterol-dependent cytolysin perfringolysin O, from the bacterium Clostridium perfringens, which selectively binds to membrane domains enriched in cholesterol; and (iv) ostreolysin, from the mushroom Pleurotus ostreatus, which does not bind to a single raft-enriched lipid component, but requires a specific combination of two of the most important raft-residing lipids: sphingomyelin and cholesterol. Nontoxic, raft-binding derivatives of cytolytic proteins have already been successfully used to explore both the structure and function of membrane rafts, and of raft-associated molecules. Here, we review these four new derivatives of pore-forming toxins as new putative markers of these membrane microdomains. PMID:23244522

Highly flexible, TpPa-1@PBI-BuI and TpBD@PBI-BuI hybrid membranes based on chemically stable covalent organic frameworks (COFs) could be obtained with the polymer. The loading obtained was substantially higher (50 %) than generally observed with MOFs. These hybrid membranes show an exciting enhancement in permeability (about sevenfold) with appreciable separation factors for CO2/N2 and CO2/CH4. Further, we found that with COF pore modulation, the gas permeability can be systematically enhanced. PMID:26865381

Porous PLA structure has been widely used in cell transplantation, drug carrier and wound dressing. The porous structure can be controlled depending on the choice of the polymer, solvent, nonsolvent and preparation parameters. In this study, the porous PLA matrix membranes were prepared by adding PEG 400 in PLA solution using dichloromethane (DCM) as solvent prior to casting. The influence of other liquids as co-solvent on pore formation and the structural change during membrane formation were evaluated. The co-solvents affected both porous topography and mechanical properties of PLA membrane. The porous matrix were produced when the non-solvent of PLA was used as co-solvent. Cryo-SEM micrographs revealed that PEG 400 still remained in the PLA porous matrix membrane. From the tracking of the structural change during film formation, the PLA-PEG solution changed into porous structure by liquid liquid phase separation and solidification processes, respectively. Thermogravimetric analysis revealed that PLA-PEG in DCM solution exhibited the two-step of weight loss, the first step occurred from DCM evaporation and the second step occurred from the degradation of PLA-PEG matrix. The liquid-liquid phase separation and solidification started when the amount of DCM was higher than PEG 400 for 2.67 folds and DCM amount was equal to that of PEG 400, respectively. These results could clarify the pore formation mechanism of porous PLA membrane and will be useful for the further investigation and application. PMID:26838905

The basal lamina or basement membrane (BM) is a key physiological system that participates in physicochemical signaling between tissue types. Its formation and function are essential in tissue maintenance, growth, angiogenesis, disease progression, and immunology. In vitro models of the BM (e.g., Boyden and transwell chambers) are common in cell biology and lab-on-a-chip devices where cells require apical and basolateral polarization. Extravasation, intravasation, membrane transport of chemokines, cytokines, chemotaxis of cells, and other key functions are routinely studied in these models. The goal of the present study was to integrate a semipermeable ultrathin polymer membrane with precisely positioned pores of 2 μm diameter in a microfluidic device with apical and basolateral chambers. We selected poly(l-lactic acid) (PLLA), a transparent biocompatible polymer, to prepare the semipermeable ultrathin membranes. The pores were generated by pattern transfer using a three-step method coupling femtosecond laser machining, polymer replication, and spin coating. Each step of the fabrication process was characterized by scanning electron microscopy to investigate reliability of the process and fidelity of pattern transfer. In order to evaluate the compatibility of the fabrication method with organs-on-a-chip technology, porous PLLA membranes were embedded in polydimethylsiloxane (PDMS) microfluidic devices and used to grow human umbilical vein endothelial cells (HUVECS) on top of the membrane with perfusion through the basolateral chamber. Viability of cells, optical transparency of membranes and strong adhesion of PLLA to PDMS were observed, thus confirming the suitability of the prepared membranes for use in organs-on-a-chip devices. PMID:27513606

Atomic layer deposition (ALD) of SiO2 onto nanoporous alumina (PA) membranes was investigated with the aim of adjusting the pore size and transport properties. PA membranes from commercial sources with a range of pore diameters (20 nm, 100 nm and 200 nm) were used and modified by atomic layer deposition using tris(tert-butoxy)silanol and water as the precursor couple. By adjusting the number of deposition cycles, the thickness of the conformal silica coating was controlled, reducing the effective pore diameter, and subsequently changing the transport properties of the PA membrane. Silica coated PA membranes with desired pore diameters from <5 nm to 100 nm were fabricated. In addition to the pore size, the transport properties and selectivity of fabricated silica coated PA membranes were controlled by chemical functionalisation using a silane with hydrophobic properties. Structural and chemical properties of modified membranes were studied by dynamic secondary ion mass spectrometry (DSIMS) and scanning electron microscopy (SEM). Spectrophotometric methods were used to evaluate the transport properties and selectivity of silica coated membranes by permeation studies of hydrophobic and hydrophilic organic molecules. The resultant silica/PA membranes with specific surface chemistry and controlled pore size are applicable for molecular separation, cell culture, bioreactors, biosensing and drug delivery.

Membranes are crucial in modern industry and both new technologies and materials need to be designed to achieve higher selectivity and performance. Exotic materials such as nanoparticles offer promising perspectives, and combining both their very high specific surface area and the possibility to incorporate them into macrostructures have already shown to substantially increase the membrane performance. In this paper we report on the fabrication and engineering of metal-reinforced carbon nanotube (CNT) Bucky-Paper (BP) composites with tuneable porosity and surface pore size. A BP is an entangled mesh non-woven like structure of nanotubes. Pure CNT BPs present both very high porosity (>90%) and specific surface area (>400 m2/g). Furthermore, their pore size is generally between 20–50 nm making them promising candidates for various membrane and separation applications. Both electro-plating and electroless plating techniques were used to plate different series of BPs and offered various degrees of success. Here we will report mainly on electroless plated gold/CNT composites. The benefit of this method resides in the versatility of the plating and the opportunity to tune both average pore size and porosity of the structure with a high degree of reproducibility. The CNT BPs were first oxidized by short UV/O3 treatment, followed by successive immersion in different plating solutions. The morphology and properties of these samples has been investigated and their performance in air permeation and gas adsorption will be reported. PMID:24957493

The prototypical antimicrobial peptide, melittin, is well-known for its ability to induce pores in zwitterionic model lipid membranes. However, the mechanism by which melittin accomplishes this is not fully understood. We have conducted all-atom and coarse-grained molecular dynamics simulations which suggest that melittin employs a highly cooperative mechanism for the induction of both small and large membranepores. The process by which this peptide induces membranepores appears to be driven by its affinity to membrane defects via its N-terminus region. In our simulations, a membrane defect was deliberately created through either lipid flip-flop or the reorientation of one adsorbed melittin peptide. In a cooperative response, other melittin molecules also inserted their N-termini into the created defect, thus lowering the overall free energy. The insertion of these peptide molecules ultimately allowed the defect to develop into a small transmembrane pore, with an estimated diameter of ∼1.5 nm and a lifetime of the order of tens of milliseconds. In the presence of a finite membrane tension, we show that this small pore can act as a nucleation site for the stochastic rupture of the lipid bilayer, so as to create a much larger pore. We found that a threshold membrane tension of 25 mN/m was needed to create a ruptured pore. Furthermore, by actively accumulating at its edge, adsorbed peptides are able to cooperatively stabilize this larger pore. The defect-mediated pore formation mechanism revealed in this work may also apply to other amphipathic membrane-active peptides. PMID:26267389

Electroporation of neurons, i.e. electric-field induced generation of membrane nanopores to facilitate internalization of molecules, is a classic technique used in basic neuroscience research and recently has been proposed as a promising therapeutic strategy in the area of neuro-oncology. To optimize electroporation parameters, optical techniques capable of delivering time and spatially-resolved information on electroporation pore formation at the nanometer scale would be advantageous. For this purpose we describe here a novel optical method based on second harmonic generation (SHG) microscopy. Due to the nonlinear and coherent nature of SHG, the 3D radiation lobes from stained neuronal membranes are sensitive to the spatial distribution of scatterers in the illuminated patch, and in particular to nanopore formation.We used phase-array analysis to computationally study the SHG signal as a function of nanopore size and nanopore population density and confirmed experimentally, in accordance with previous work, the dependence of nanopore properties on membrane location with respect to the electroporation electric field; higher nanopore densities, lasting < 5 milliseconds, are observed at membrane patches perpendicular to the field whereas lower density is observed at partly tangent locations. Differences between near-anode and near-cathode cell poles are also measured, showing higher pore densities at the anodic pole compared to cathodic pole. This technique is promising for the study of nanopore dynamics in neurons and for the optimization of novel electroporation-based therapeutic approaches. PMID:21339876

Inflammatory caspases (caspases 1, 4, 5 and 11) are activated in response to microbial infection and danger signals. When activated, they cleave mouse and human gasdermin D (GSDMD) after Asp276 and Asp275, respectively, to generate an N-terminal cleavage product (GSDMD-NT) that triggers inflammatory death (pyroptosis) and release of inflammatory cytokines such as interleukin-1β. Cleavage removes the C-terminal fragment (GSDMD-CT), which is thought to fold back on GSDMD-NT to inhibit its activation. However, how GSDMD-NT causes cell death is unknown. Here we show that GSDMD-NT oligomerizes in membranes to form pores that are visible by electron microscopy. GSDMD-NT binds to phosphatidylinositol phosphates and phosphatidylserine (restricted to the cell membrane inner leaflet) and cardiolipin (present in the inner and outer leaflets of bacterial membranes). Mutation of four evolutionarily conserved basic residues blocks GSDMD-NT oligomerization, membrane binding, pore formation and pyroptosis. Because of its lipid-binding preferences, GSDMD-NT kills from within the cell, but does not harm neighbouring mammalian cells when it is released during pyroptosis. GSDMD-NT also kills cell-free bacteria in vitro and may have a direct bactericidal effect within the cytosol of host cells, but the importance of direct bacterial killing in controlling in vivo infection remains to be determined. PMID:27383986

We investigated the effects of electrostatic interactions on the rate constant (kp) for tension-induced pore formation in lipid membranes of giant unilamellar vesicles under constant applied tension. A decrease in salt concentration in solution as well as an increase in surface charge density of the membranes increased kp. These data indicate that kp increases as the extent of electrostatic interaction increases. We developed a theory on the effect of the electrostatic interactions on the free energy profile of the membrane containing a prepore and also on the values of kp; this theory explains the experimental results and fits the experimental data reasonably well in the presence of weak electrostatic interactions. Based on these results, we conclude that a decrease in the free energy barrier of the prepore state due to electrostatic interactions is the main factor causing an increase in kp.

Polymer membranes with well-controlled and vertically oriented pores are of great importance in the applications for water treatment and tissue engineering. On the basis of two-dimensional solvent freezing, we report environmentally friendly facile fabrication of such membranes from a broad spectrum of polymer resources including poly(vinylidene fluoride), poly(l-lactic acid), polyacrylonitrile, polystyrene, polysulfone and polypropylene. Dimethyl sulfone, diphenyl sulfone, and arachidic acid are selected as green solvents crystallized in the polymer matrices under two-dimensional temperature gradients induced by water at ambient temperature. Parallel Monte Carlo simulations of the lattice polymers demonstrate that the directional process is feasible for each polymer holding suitable interaction with a corresponding solvent. As a typical example of this approach, poly(vinylidene fluoride) membranes exhibit excellent tensile strength, high optical transparence, and outstanding separation performance for the mixtures of yeasts and lactobacilli. PMID:27188247

A flexible membrane with sub-5 nm single-walled carbon nanotube (SWNT) pores is developed by F. Fornasiero and co-workers, as described on page 5871, for application as a key component of protective, yet breathable fabrics. The SWNTs are shown to enable exceptionally fast transport of water vapor under a concentration driving force. Thus, membranes having SWNTs as moisture-conductive pores feature outstanding breathability and provide a high degree of protection from biological threats by size exclusion. PMID:27442972

Interaction between bacterial toxins and cellular surface receptors is an important component of the host-pathogen interaction. Anthrax toxin protective antigen (PA) binds to the cell surface receptor, enters the cell through receptor-mediated endocytosis, and forms a pore on the endosomal membrane that translocates toxin enzymes into the cytosol of the host cell. As the major receptor for anthrax toxin in vivo, anthrax toxin receptor 2 (ANTXR2) plays an essential role in anthrax toxin action by providing the toxin with a high-affinity binding anchor on the cell membrane and a path of entry into the host cell. ANTXR2 also acts as a molecular clamp by shifting the pH threshold of PA pore formation to a more acidic pH range, which prevents premature pore formation at neutral pH before the toxin reaches the designated intracellular location. Most recent studies have suggested that the disulfide bond in the immunoglobulin (Ig)-like domain of ANTXR2 plays an essential role in anthrax toxin action. Here we will review the roles of ANTXR2 in anthrax toxin action, with an emphasis on newly updated knowledge. PMID:26805886

Summary BAK activation represents a key step during apoptosis, but how it converts into a mitochondria-permeabilizing pore remains unclear. By further delineating the structural rearrangements involved, we reveal that BAK activation progresses through a series of independent steps: BH3-domain exposure, N-terminal change, oligomerization, and membrane insertion. Employing a “BCL-XL-addiction” model, we show that neutralization of BCL-XL by the BH3 mimetic ABT-737 resulted in death only when cells were reconstituted with BCL-XL:BAK, but not BCL-2/ BCL-XL:BIM complexes. Although this resembles the indirect model, release of BAK from BCL-XL did not result in spontaneous adoption of the pore conformation. Commitment to apoptosis required association of the direct activator BIM with oligomeric BAK promoting its conversion to a membrane-inserted pore. The sequential nature of this cascade provides multiple opportunities for other BCL-2 proteins to interfere with or promote BAK activation and unites aspects of the indirect and direct activation models. PMID:24120870

Interaction between bacterial toxins and cellular surface receptors is an important component of the host-pathogen interaction. Anthrax toxin protective antigen (PA) binds to the cell surface receptor, enters the cell through receptor-mediated endocytosis, and forms a pore on the endosomal membrane that translocates toxin enzymes into the cytosol of the host cell. As the major receptor for anthrax toxin in vivo, anthrax toxin receptor 2 (ANTXR2) plays an essential role in anthrax toxin action by providing the toxin with a high-affinity binding anchor on the cell membrane and a path of entry into the host cell. ANTXR2 also acts as a molecular clamp by shifting the pH threshold of PA pore formation to a more acidic pH range, which prevents premature pore formation at neutral pH before the toxin reaches the designated intracellular location. Most recent studies have suggested that the disulfide bond in the immunoglobulin (Ig)-like domain of ANTXR2 plays an essential role in anthrax toxin action. Here we will review the roles of ANTXR2 in anthrax toxin action, with an emphasis on newly updated knowledge. PMID:26805886

Sticholysins (Sts) I and II (StI/II) are pore-forming toxins (PFTs) produced by the Caribbean Sea anemone Stichodactyla helianthus belonging to the actinoporin family, a unique class of eukaryotic PFTs exclusively found in sea anemones. The role of lipid phase co-existence in the mechanism of the action of membranolytic proteins and peptides is not clearly understood. As for actinoporins, it has been proposed that phase separation promotes pore forming activity. However little is known about the effect of sticholysins on the phase separation of lipids in membranes. To gain insight into the mechanism of action of sticholysins, we evaluated the effect of these proteins on lipid segregation using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). New evidence was obtained reflecting that these proteins reduce line tension in the membrane by promoting lipid mixing. In terms of the relevance for the mechanism of action of actinoporins, we hypothesize that expanding lipid disordered phases into lipid ordered phases decreases the lipid packing at the borders of the lipid raft, turning it into a more suitable environment for N-terminal insertion and pore formation. PMID:23954588

The surface morphology of several Cyclopore filters, consisting of thin track-etched sheets of polycarbonate, is analyzed here. Scanning electron microscopy and computerized image analysis have been applied. The surface porosity and the pore density or number of pores per surface unit are directly obtained for each filter, while the statistical distribution of the pore areas, pore perimeters, equivalent pore diameters, and pore shape factors are studied as well. These pore size distributions have been studied for six types of filters (C01, C02, C04, C06, C08, and C10) and the existence of a relevant portion of double and other multiple pores has been revealed. The fraction of these multiple pores are correlated with the nominal pore radii. The results on pore size have been used to predict the volume flows of the membranes studied. This can be done only by assuming that the surface characteristics remain unchanged in the internal volume of the filters, which leads to hydrodynamic radii well in accordance with the experimental ones, within the error range. Nevertheless, it seems that some of the pores should have internal widenings with inner radii close to 120% of the external ones.

To investigate the role of the fusogenic protein in the initial size and dynamics of the pore that widens to finalize membrane fusion, two different fusion proteins expressed in the same cell line were investigated: the major glycoprotein of baculovirus Autographa californica (GP64) and the hemaggluttinin of influenza X31 (HA). The host Sf9 cells expressing these viral proteins, irrespective of protein species, fused to human red blood cells (RBC) upon acidification of the medium. High time resolution electrophysiological study of fusion pore conductance revealed fundamental differences in a) the initial pore conductance (pores created by HA were smaller than those created by GP64), b) the ability of pores to flicker (only HA-mediated pores flickered), and c) the time required for pore formation (HA-mediated pores took much longer to form following acidification). Thus 1) HA and GP64 have divergent electrophysiological phenotypes even when they fuse identical membranes, and 2) fusion proteins play a crucial role in determining initial fusion pore characteristics. The structure of the initial fusion pore detected by electrical conductance measurements is sensitive to the nature of the fusion protein. PMID:18208404

The quantitative characterization of pore structure of Sartobind Q, a strongly basic membrane anion exchanger that is formed by cross-linked cellulose support and a hydrogel layer on its pore surface, was made combining the results obtained by several experimental techniques: liquid impregnation, batch size-exclusion, inverse size-exclusion chromatography, and permeability. Mercury intrusion and nitrogen sorption porosimetry were carried out for a dry cellulose support membrane in order to get additional information for building a model of the bimodal pore structure. The model incorporated the distribution of the total pore volume between transport and gel-layer pores and the partitioning of solutes of different molecular weights was expressed through the cylindrical pore model for the transport pores and random plane model for the gel layer. The effect of composition of liquid phase on the pore structure was investigated in redistilled water, phosphate and Tris-HCl buffers containing up to 1M NaCl. Evident differences in the bimodal pore structure were observed here when both the specific volume and size of the hydrogel layer pores significantly decreased with the ionic strength of liquid phase. PMID:19117574

Membrane-based separation processes have been used extensively for drinking water purification, wastewater treatment, and numerous other applications. More recent developments in membrane functionalization have made the use of membrane science important in diverse fields, from tunable separations to catalysis. The focus of this work is to create a common membrane platform for the incorporation of technologies capable of degrading target pollutants. Functionalized membranes capable of metal capture were created using water-based and solvent-based acrylic acid polymerization to synthesize poly (acrylic acid) (PAA) within poly(vinylidene fluoride) (PVDF) membranepores. The COO− groups of PAA were used to capture Fe(II), which was then either reduced and doped with Pd to form Fe/Pd nanoparticles or used as-is for free radical generation with hydrogen peroxide. Fe/Pd nanoparticles were synthesized within the pores of a PAA/PVDFmembrane functionalized via aqueous (green) chemistry and used to dechlorinate trichloroethylene (TCE) and 2,2′-dichlorobiphenyl (DiCB). A PAA/PVDFmembrane containing immobilized Fe(III) was used to obtain controlled free radical generation and target organic (pentachlorophenol) degradation within the membranepore under convective flow conditions. PMID:20556223

Poly (vinylidene fluoride) (PVDF) with "living" poly (acrylic acid) (PAAc) side chains (PVDF-g-PAAc) was prepared by reversible addition-fragmentation chain transfer (RAFT)-mediated graft copolymerization of acrylic acid (AAc) with the ozone-pretreated PVDF. The chemical composition and structure of the copolymers were characterized by elemental analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The copolymer could be readily cast into pH-sensitive microfiltration (MF) membranes with enriched living PAAc graft chains on the surface (including the pore surfaces) by phase inversion in an aqueous medium. The surface composition of the membranes was determined by X-ray photoelectron spectroscopy. The morphology of the membranes was characterized by scanning electron microscopy. The pore size distribution of the membranes was found to be much more uniform than that of the corresponding membranes cast from PVDF-g-PAAc prepared by the "conventional" free-radical graft copolymerization process. Most important of all, the MF membranes with surface-tethered PAAc macro chain transfer agents, or the living membrane surfaces, could be further functionalized via surface-initiated block copolymerization with N-isopropylacrylamide (NIPAAM) to obtain the PVDF-g-PAAc-b-PNIPAAM MF membranes, which exhibited both pH- and temperature-dependent permeability to aqueous media. PMID:16459627

The recently identified TMEM16/anoctamin protein family includes Ca(2+)-activated anion channels (TMEM16A, TMEM16B), a cation channel (TMEM16F) and proteins with unclear function. TMEM16 channels consist of eight putative transmembrane domains (TMs) with TM5-TM6 flanking a re-entrant loop thought to form the pore. In TMEM16A this region has also been suggested to contain residues involved in Ca(2+) binding. The role of the putative pore-loop of TMEM16 channels was investigated using a chimeric approach. Heterologous expression of either TMEM16A or TMEM16B resulted in whole-cell anion currents with very similar conduction properties but distinct kinetics and degrees of sensitivity to Ca(2+). Furthermore, whole-cell currents mediated by TMEM16A channels were ∼six times larger than TMEM16B-mediated currents. Replacement of the putative pore-loop of TMEM16A with that of TMEM16B (TMEM16A-B channels) reduced the currents by ∼six-fold, while the opposite modification (TMEM16B-A channels) produced a ∼six-fold increase in the currents. Unexpectedly, these changes were not secondary to variations in channel gating by Ca(2+) or voltage, nor were they due to changes in single-channel conductance. Instead, they depended on the number of functional channels present on the plasma membrane. Generation of additional, smaller chimeras within the putative pore-loop of TMEM16A and TMEM16B led to the identification of a region containing a non-canonical trafficking motif. Chimeras composed of the putative pore-loop of TMEM16F transplanted into the TMEM16A protein scaffold did not conduct anions or cations. These data suggest that the putative pore-loop does not form a complete, transferable pore domain. Furthermore, our data reveal an unexpected role for the putative pore-loop of TMEM16A and TMEM16B channels in the control of the whole-cell Ca(2+)-activated Cl(-) conductance. PMID:23613533

Three major outer membrane proteins with apparent molecular masses of 43, 45, and 51 kDa were purified from Wolinella recta ATCC 33238, and their pore-forming abilities were determined by the black lipid bilayer method. The non-heat-modifiable 45-kDa protein (Omp 45) showed no pore-forming activity even at high KCl concentrations. The single-channel conductances in 1 M KCl of the heat-modifiable proteins with apparent molecular masses of 43 kDa (Omp 43) and 51 kDa (Omp 51) were 0.49 and 0.60 nS, respectively. The proteins formed nonselective channels and, as determined by experiments of ion selectivity and zero-current potential, were weakly anion selective. Images PMID:1370429

Lysenin from the coelomic fluid of the earthworm Eisenia fetida belongs to the aerolysin family of small β-pore-forming toxins (β-PFTs), some members of which are pathogenic to humans and animals. Despite efforts, a high-resolution structure of a channel for this family of proteins has been elusive and therefore the mechanism of activation and membrane insertion remains unclear. Here we determine the pore structure of lysenin by single particle cryo-EM, to 3.1 Å resolution. The nonameric assembly reveals a long β-barrel channel spanning the length of the complex that, unexpectedly, includes the two pre-insertion strands flanking the hypothetical membrane-insertion loop. Examination of other members of the aerolysin family reveals high structural preservation in this region, indicating that the membrane-insertion pathway in this family is conserved. For some toxins, proteolytic activation and pro-peptide removal will facilitate unfolding of the pre-insertion strands, allowing them to form the β-barrel of the channel. PMID:27048994

Lysenin from the coelomic fluid of the earthworm Eisenia fetida belongs to the aerolysin family of small β-pore-forming toxins (β-PFTs), some members of which are pathogenic to humans and animals. Despite efforts, a high-resolution structure of a channel for this family of proteins has been elusive and therefore the mechanism of activation and membrane insertion remains unclear. Here we determine the pore structure of lysenin by single particle cryo-EM, to 3.1 Å resolution. The nonameric assembly reveals a long β-barrel channel spanning the length of the complex that, unexpectedly, includes the two pre-insertion strands flanking the hypothetical membrane-insertion loop. Examination of other members of the aerolysin family reveals high structural preservation in this region, indicating that the membrane-insertion pathway in this family is conserved. For some toxins, proteolytic activation and pro-peptide removal will facilitate unfolding of the pre-insertion strands, allowing them to form the β-barrel of the channel.

Lysenin from the coelomic fluid of the earthworm Eisenia fetida belongs to the aerolysin family of small β-pore-forming toxins (β-PFTs), some members of which are pathogenic to humans and animals. Despite efforts, a high-resolution structure of a channel for this family of proteins has been elusive and therefore the mechanism of activation and membrane insertion remains unclear. Here we determine the pore structure of lysenin by single particle cryo-EM, to 3.1 Å resolution. The nonameric assembly reveals a long β-barrel channel spanning the length of the complex that, unexpectedly, includes the two pre-insertion strands flanking the hypothetical membrane-insertion loop. Examination of other members of the aerolysin family reveals high structural preservation in this region, indicating that the membrane-insertion pathway in this family is conserved. For some toxins, proteolytic activation and pro-peptide removal will facilitate unfolding of the pre-insertion strands, allowing them to form the β-barrel of the channel. PMID:27048994

B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax) is a member of the Bcl-2 protein family having a pivotal role in triggering cell commitment to apoptosis. Bax is latent and monomeric in the cytosol but transforms into its lethal, mitochondria-embedded oligomeric form in response to cell stress, leading to the release of apoptogenic factors such as cytochrome C. Here, we dissected the structural correlates of Bax membrane insertion while oligomerization is halted. This strategy was enabled through the use of nanometer-scale phospholipid bilayer islands (nanodiscs) the size of which restricts the reconstituted system to single Bax-molecule activity. Using this minimal reconstituted system, we captured structural correlates that precede Bax homo-oligomerization elucidating previously inaccessible steps of the core molecular mechanism by which Bcl-2 family proteins regulate membrane permeabilization. We observe that, in the presence of BH3 interacting domain death agonist (Bid) BH3 peptide, Bax monomers induce the formation of ∼3.5-nm diameter pores and significantly distort the phospholipid bilayer. These pores are compatible with promoting release of ions as well as proteinaceous components, suggesting that membrane-integrated Bax monomers in the presence of Bid BH3 peptides are key functional units for the activation of the cell demolition machinery. PMID:23788040

Mitochondrial outer membrane permeabilization (MOMP) is a critical step in apoptosis and is regulated by Bcl-2 family proteins. In vitro systems using cardiolipin-containing liposomes have demonstrated the key features of MOMP induced by Bax and cleaved Bid; however, the nature of the “pores” and how they are formed remain obscure. We found that mitochondrial outer membranes contained very little cardiolipin, far less than that required for liposome permeabilization, despite their responsiveness to Bcl-2 family proteins. Strikingly, the incorporation of isolated mitochondrial outer membrane (MOM) proteins into liposomes lacking cardiolipin conferred responsiveness to cleaved Bid and Bax. Cardiolipin dependence was observed only when permeabilization was induced with cleaved Bid but not with Bid or Bim BH3 peptide or oligomerized Bax. Therefore, we conclude that MOM proteins specifically assist cleaved Bid in Bax-mediated permeabilization. Cryoelectron microscopy of cardiolipin-liposomes revealed that cleaved Bid and Bax produced large round holes with diameters of 25–100 nm, suggestive of lipidic pores. In sum, we propose that activated Bax induces lipidic pore formation and that MOM proteins assist cleaved Bid in this process in the absence of cardiolipin. PMID:19244344

B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax) is a member of the Bcl-2 protein family having a pivotal role in triggering cell commitment to apoptosis. Bax is latent and monomeric in the cytosol but transforms into its lethal, mitochondria-embedded oligomeric form in response to cell stress, leading to the release of apoptogenic factors such as cytochrome C. Here, we dissected the structural correlates of Bax membrane insertion while oligomerization is halted. This strategy was enabled through the use of nanometer-scale phospholipid bilayer islands (nanodiscs) the size of which restricts the reconstituted system to single Bax-molecule activity. Using this minimal reconstituted system, we captured structural correlates that precede Bax homo-oligomerization elucidating previously inaccessible steps of the core molecular mechanism by which Bcl-2 family proteins regulate membrane permeabilization. We observe that, in the presence of BH3 interacting domain death agonist (Bid) BH3 peptide, Bax monomers induce the formation of ~3.5-nm diameter pores and significantly distort the phospholipid bilayer. These pores are compatible with promoting release of ions as well as proteinaceous components, suggesting that membrane-integrated Bax monomers in the presence of Bid BH3 peptides are key functional units for the activation of the cell demolition machinery. PMID:23788040

Gasdermin-D (GsdmD) is a critical mediator of innate immune defense because its cleavage by the inflammatory caspases 1, 4, 5, and 11 yields an N-terminal p30 fragment that induces pyroptosis, a death program important for the elimination of intracellular bacteria. Precisely how GsdmD p30 triggers pyroptosis has not been established. Here we show that human GsdmD p30 forms functional pores within membranes. When liberated from the corresponding C-terminal GsdmD p20 fragment in the presence of liposomes, GsdmD p30 localized to the lipid bilayer, whereas p20 remained in the aqueous environment. Within liposomes, p30 existed as higher-order oligomers and formed ring-like structures that were visualized by negative stain electron microscopy. These structures appeared within minutes of GsdmD cleavage and released Ca2+ from preloaded liposomes. Consistent with GsdmD p30 favoring association with membranes, p30 was only detected in the membrane-containing fraction of immortalized macrophages after caspase-11 activation by lipopolysaccharide. We found that the mouse I105N/human I104N mutation, which has been shown to prevent macrophage pyroptosis, attenuated both cell killing by p30 in a 293T transient overexpression system and membrane permeabilization in vitro, suggesting that the mutants are actually hypomorphs, but must be above certain concentration to exhibit activity. Collectively, our data suggest that GsdmD p30 kills cells by forming pores that compromise the integrity of the cell membrane. PMID:27339137

Gasdermin-D (GsdmD) is a critical mediator of innate immune defense because its cleavage by the inflammatory caspases 1, 4, 5, and 11 yields an N-terminal p30 fragment that induces pyroptosis, a death program important for the elimination of intracellular bacteria. Precisely how GsdmD p30 triggers pyroptosis has not been established. Here we show that human GsdmD p30 forms functional pores within membranes. When liberated from the corresponding C-terminal GsdmD p20 fragment in the presence of liposomes, GsdmD p30 localized to the lipid bilayer, whereas p20 remained in the aqueous environment. Within liposomes, p30 existed as higher-order oligomers and formed ring-like structures that were visualized by negative stain electron microscopy. These structures appeared within minutes of GsdmD cleavage and released Ca(2+) from preloaded liposomes. Consistent with GsdmD p30 favoring association with membranes, p30 was only detected in the membrane-containing fraction of immortalized macrophages after caspase-11 activation by lipopolysaccharide. We found that the mouse I105N/human I104N mutation, which has been shown to prevent macrophage pyroptosis, attenuated both cell killing by p30 in a 293T transient overexpression system and membrane permeabilization in vitro, suggesting that the mutants are actually hypomorphs, but must be above certain concentration to exhibit activity. Collectively, our data suggest that GsdmD p30 kills cells by forming pores that compromise the integrity of the cell membrane. PMID:27339137

Nanofibrillated cellulose (NFC) is a natural fibrous material that can be readily processed into membranes. NFC membranes for fluid separation work in aqueous medium, thus in their swollen state. The present study is devoted to a critical investigation of porosity, pore volume, specific surface area, and pore size distribution of dry and wet NFC nanopapers, also known as membranes, with various established techniques, such as electron microscopy, helium pycnometry, mercury intrusion, gas adsorption (N2 and Kr), and thermoporometry. Although these techniques can be successfully applied to inorganic materials (e.g., mesoporous silica), it is necessary to appraise them for organic and hydrophilic products such as NFC membranes. This is due to different phenomena occurring at the materials interfaces with the probing fluids. Mercury intrusion and gas adsorption are often used for the characterization of porosity-related properties; nevertheless, both techniques characterize materials in the dry state. In parallel, thermoporometry was employed to monitor the structure changes upon swelling, and a water permeance test was run to show the accessibility of the membranes to fluids. For the first time, the methods were systematically screened, and we highlighted the need of uniform sample treatments prior to the measurements (i.e., sample cutting and outgassing protocols) in order to harmonize results from the literature. The need for revising the applicability range of mercury intrusion and the inappropriateness of nitrogen adsorption were pointed out. We finally present a table for selecting the most appropriate method to determine a desired property and propose guidelines for results interpretation from which future users could profit. PMID:26516781

We report ion channel formation by chemotherapy drugs: thiocolchicoside (TCC) and taxol (TXL) which primarily target tubulin but not only. For example, TCC has been shown to interact with GABAA, nuclear envelope and strychnine-sensitive glycine receptors. TXL interferes with the normal breakdown of microtubules inducing mitotic block and apoptosis. It also interacts with mitochondria and found significant chemotherapeutic applications for breast, ovarian and lung cancer. In order to better understand the mechanisms of TCC and TXL actions, we examined their effects on phospholipid bilayer membranes. Our electrophysiological recordings across membranes constructed in NaCl aqueous phases consisting of TCC or TXL under the influence of an applied transmembrane potential (V) indicate that both molecules induce stable ion flowing pores/channels in membranes. Their discrete current versus time plots exhibit triangular shapes which is consistent with a spontaneous time-dependent change of the pore conductance in contrast to rectangular conductance events usually induced by ion channels. These events exhibit conductance (~0.01-0.1 pA/mV) and lifetimes (~5-30 ms) within the ranges observed in e.g., gramicidin A and alamethicin channels. The channel formation probability increases linearly with TCC/TXL concentration and V and is not affected by pH (5.7 - 8.4). A theoretical explanation on the causes of chemotherapy drug induced ion pore formation and the pore stability has also been found using our recently discovered binding energy between lipid bilayer and the bilayer embedded ion channels using gramicidin A channels as tools. This picture of energetics suggests that as the channel forming agents approach to the lipids on bilayer the localized charge properties in the constituents of both channel forming agents (e.g., chemotherapy drugs in this study) and the lipids determine the electrostatic drug-lipid coupling energy through screened Coulomb interactions between the drug

Background In several neurodegenerative diseases, hyperphosphorylation at position Ser129 is found in fibrillar deposits of alpha-synuclein (asyn), implying a pathophysiological role of asyn phosphorylation in neurodegeneration. However, recent animal models applying asyn phosphorylation mimics demonstrated a protective effect of phosphorylation. Since metal-ion induced asyn oligomers were identified as a potential neurotoxic aggregate species with membranepore-forming abilities, the current study was undertaken to determine effects of asyn phosphorylation on oligomer membrane binding. Methods We investigated the influence of S129 phosphorylation on interactions of metal-ion induced asyn oligomers with small unilamellar lipid vesicles (SUV) composed of POPC and DPPC applying the phosphorylation mimic asyn129E. Confocal single-particle fluorescence techniques were used to monitor membrane binding at the single-particle level. Results Binding of asyn129E monomers to gel-state membranes (DPPC-SUV) is slightly reduced compared to wild-type asyn, while no interactions with membranes in the liquid-crystalline state (POPC-SUV) are seen for both asyn and asyn129E. Conversely, metal-ion induced oligomer formation is markedly increased in asyn129E. Surprisingly, membrane binding to POPC-SUV is nearly absent in Fe3+ induced asyn129E oligomers and markedly reduced in Al3+ induced oligomers. Conclusion The protective effect of pseudophosphorylation seen in animal models may be due to impeded oligomer membrane binding. Phosphorylation at Ser129 may thus have a protective effect against neurotoxic asyn oligomers by preventing oligomer membrane binding and disruption of the cellular electrophysiological equilibrium. Importantly, these findings put a new complexion on experimental pharmaceutical interventions against POLO-2 kinase. PMID:24911099

There is increasing demand to functionalize meso- and nanoporous materials by coating and make the porous substrate biocompatible or environmentally friendly. However, coating on a meso-porous substrate poses great challenges, especially if the pore aspect ratio is high. We adopted the pulsed laser deposition (PLD) method to coat Ni3Al-based meso-porous membranes, which were fabricated from a single-crystal Ni-based superalloy by a unique selective phase dissolution technique. These membranes were about 250 µm thick and had channel-like pores (~200 nm wide) with very high aspect ratio. Two different coating materials, i.e. diamond-like carbon (DLC) and titanium, were used to coat these membranes. High energy C or Ti ions, produced in the plasma plume by the PLD process, penetrated the channel-like pores and deposited coatings on the pore walls deep inside the membrane. The thickness and the quality of coatings on the pore walls were examined using the dual-beam system. The coating thickness, of the order of 50 nm, was adherent to the pore walls and was quite uniform at different depths. The carbon and the Ti deposition behaved quite similarly. The preliminary experiments showed that the PLD is an adequate method for coating fine open cavities of complex geometry. Simulations based on stopping and the range of ions in matter (SRIM) calculations helped in understanding the deposition processes on pore walls at great depths.

The 121-kDa poremembrane protein (POM121) is a bitopic integral membrane protein specifically located in the poremembrane domain of the nuclear envelope with its short N-terminal tail exposed on the luminal side and its major C-terminal portion adjoining the nuclear pore complex. In order to locate a signal for targeting of POM121 to the nuclear pores, we overexpressed selected regions of POM121 alone or fused to the green fluorescent protein (GFP) in transiently transfected COS-1 cells or in a stably transfected neuroblastoma cell line. Microscopic analysis of the GFP fluorescence or immunostaining was used to determine the intracellular distribution of the overexpressed proteins. The endofluorescent GFP tag had no effect on the distribution of POM121, since the chimerical POM121-GFP fusion protein was correctly targeted to the nuclear pores of both COS-1 cells and neuroblastoma cells. Based on the differentiated intracellular sorting of the POM121 variants, we conclude that the first 128 amino acids of POM121 contains signals for targeting to the continuous endoplasmic reticulum/nuclear envelope membrane system but not specifically to the nuclear pores and that a specific nuclear pore targeting signal is located between amino acids 129 and 618 in the endoplasmically exposed portion of POM121. PMID:9461306

Pore-forming toxins are an important group of natural molecules that damage cellular membranes by forming transmembrane pores. They are used by many organisms for attack or defense and similar proteins are employed in the immune system of vertebrates. Various biophysical approaches have been used to understand how these proteins act at the molecular level. One of the most useful, in terms of monitoring pore formation in real time, is a method that employs planar lipid membranes and involves ionic current measurements. Here we highlight the advantages and possibilities that this approach offers and show how it can advance understanding of the pore-forming mechanism and pore properties for one of the most important families of natural toxins, the cholesterol-dependent cytolysins. PMID:23876488

ABSTRACT Membrane-active peptides, components of capsid structural proteins, assist viruses in overcoming the host membrane barrier in the initial stages of infection. Several such peptides have been identified, and their roles in membrane fusion or disruption have been characterized through biophysical studies. In several members of the Picornaviridae family, the role of the VP4 structural peptide in cellular-membrane penetration is well established. However, there is not much information on the membrane-penetrating capsid components of hepatitis A virus (HAV), an unusual member of this family. The VP4 peptide of HAV differs from its analogues in other picornaviruses in being significantly shorter in length and in lacking a signal for myristoylation, thought to be a critical requisite for VP4-mediated membrane penetration. Here we report, for the first time, that the atypical VP4 in HAV contains significant membrane-penetrating activity. Using a combination of biophysical assays and molecular dynamics simulation studies, we show that VP4 integrates into membrane vesicles through its N-terminal region to finally form discrete pores of 5- to 9-nm diameter, which induces leakage in the vesicles without altering their overall size or shape. We further demonstrate that the membrane activity of VP4 is specific toward vesicles mimicking the lipid content of late endosomes at acidic pH. Taken together, our data indicate that VP4 might be essential for the penetration of host endosomal membranes and release of the viral genome during HAV entry. IMPORTANCE Hepatitis A virus causes acute hepatitis in humans through the fecal-oral route and is particularly prevalent in underdeveloped regions with poor hygienic conditions. Although a vaccine for HAV exists, its high cost makes it unsuitable for universal application in developing countries. Studies on host-virus interaction for HAV have been hampered due to a lack of starting material, since the virus is extremely slow growing

We report the intergrowth of ZIF-8 crystals on ultrathin graphene oxide (GO) membranes, which helps to reduce the non-selective pores of pristine GO membranes leading to gas selectivities as high as 406, 155, and 335 for H2/CO2, H2/N2, and H2/CH4 mixtures, respectively. PMID:27181340

Most bacteriophages are tailed bacteriophages with an isometric or a prolate head attached to a long contractile, long non-contractile, or short non-contractile tail. The tail is a complex machine that plays a central role in host cell recognition and attachment, cell wall and membrane penetration, and viral genome ejection. The mechanisms involved in the penetration of the inner host cell membrane by bacteriophage tails are not well understood. Here we describe structural and functional studies of the bacteriophage ϕ29 tail knob protein gene product 9 (gp9). The 2.0 Å crystal structure of gp9 shows that six gp9 molecules form a hexameric tube structure with six flexible hydrophobic loops blocking one end of the tube before DNA ejection. Sequence and structural analyses suggest that the loops in the tube could be membrane active. Further biochemical assays and electron microscopy structural analyses show that the six hydrophobic loops in the tube exit upon DNA ejection and form a channel that spans the lipid bilayer of the membrane and allows the release of the bacteriophage genomic DNA, suggesting that cell membrane penetration involves a pore-forming mechanism similar to that of certain non-enveloped eukaryotic viruses. A search of other phage tail proteins identified similar hydrophobic loops, which indicates that a common mechanism might be used for membrane penetration by prokaryotic viruses. These findings suggest that although prokaryotic and eukaryotic viruses use apparently very different mechanisms for infection, they have evolved similar mechanisms for breaching the cell membrane. PMID:27309813

Nuclear pore complexes (NPCs) allow selective import and export while forming a barrier for untargeted proteins. Using fluorescence microscopy, we measured in vivo the permeability of the Saccharomyces cerevisiae NPC for multidomain proteins of different sizes and found that soluble proteins of 150 kDa and membrane proteins with an extralumenal domain of 90 kDa were still partly localized in the nucleus on a time scale of hours. The NPCs thus form only a weak barrier for the majority of yeast proteins, given their monomeric size. Using FGΔ-mutant strains, we showed that specific combinations of Nups, especially with Nup100, but not the total mass of FG-nups per pore, were important for forming the barrier. Models of the disordered phase of wild-type and mutant NPCs were generated using a one bead per amino acid molecular dynamics model. The permeability measurements correlated with the density predictions from coarse-grained molecular dynamics simulations in the center of the NPC. The combined in vivo and computational approach provides a framework for elucidating the structural and functional properties of the permeability barrier of nuclear pore complexes. PMID:25631821

Membrane capacitive deionization (MCDI) is a technology for water desalination based on applying an electrical field between two oppositely placed porous electrodes. Ions are removed from the water flowing through a channel in between the electrodes and are stored inside the electrodes. Ion-exchange membranes are placed in front of the electrodes allowing for counterion transfer from the channel into the electrode, while retaining the coions inside the electrode structure. We set up an extended theory for MCDI which includes in the description for the porous electrodes not only the electrostatic double layers (EDLs) formed inside the porous (carbon) particles, but also incorporates the role of the transport pathways in the electrode, i.e., the interparticle pore space. Because in MCDI the coions are inhibited from leaving the electrode region, the interparticle porosity becomes available as a reservoir to store salt, thereby increasing the total salt storage capacity of the porous electrode. A second advantage of MCDI is that during ion desorption (ion release) the voltage can be reversed. In that case the interparticle porosity can be depleted of counterions, thereby increasing the salt uptake capacity and rate in the next cycle. In this work, we compare both experimentally and theoretically adsorption/desorption cycles of MCDI for desorption at zero voltage as well as for reversed voltage, and compare with results for CDI. To describe the EDL-structure a novel modified Donnan model is proposed valid for small pores relative to the Debye length. PMID:21592485

Summary The development of low energy cost membranes to separate He from noble gas mixtures is highly desired. In this work, we studied He purification using recently experimentally realized, two-dimensional stanene (2D Sn) and decorated 2D Sn (SnH and SnF) honeycomb lattices by density functional theory calculations. To increase the permeability of noble gases through pristine 2D Sn at room temperature (298 K), two practical strategies (i.e., the application of strain and functionalization) are proposed. With their high concentration of large pores, 2D Sn-based membrane materials demonstrate excellent helium purification and can serve as a superior membrane over traditionally used, porous materials. In addition, the separation performance of these 2D Sn-based membrane materials can be significantly tuned by application of strain to optimize the He purification properties by taking both diffusion and selectivity into account. Our results are the first calculations of He separation in a defect-free honeycomb lattice, highlighting new interesting materials for helium separation for future experimental validation. PMID:26885459

The molecular basis for the effectiveness of arginine-rich cell penetrating peptides (ARCPPs) traversing a cell membrane barrier is not well established. The fact that a threshold concentration of ARCPPs is required for efficient translocation in model membranes suggests cooperative action by ARCPPs. We used umbrella sampling simulations to calculate the free energies for membranepore formation. Membrane-bound octaarginine (ARG8) peptides showed little cooperativity in lowering the free energy barrier to generate membranepores by direct peptide translocation or by lipid flip-flop. Instead, high concentrations of ARG8 peptides were found to expand the surface area of the lipid bilayer due to the deep partitioning of guanidinium ions into the lipid glycerol regions. Surface-bound ARG8 peptides can also insert an arginine side chain into one existing transient membranepore, and the lifetime of the transient membranepore is significantly extended by arginine. This suggests a cooperative kinetic mechanism may act above a threshold adsorption concentration to facilitate the rapid uptake of these peptides. PMID:25166723

The mechanism of bilayer unification in biological fusion is unclear. We reversibly arrested hemagglutinin (HA)-mediated cell–cell fusion right before fusion pore opening. A low-pH conformation of HA was required to form this intermediate and to ensure fusion beyond it. We present evidence indicating that outer monolayers of the fusing membranes were merged and continuous in this intermediate, but HA restricted lipid mixing. Depending on the surface density of HA and the membrane lipid composition, this restricted hemifusion intermediate either transformed into a fusion pore or expanded into an unrestricted hemifusion, without pores but with unrestricted lipid mixing. Our results suggest that restriction of lipid flux by a ring of activated HA is necessary for successful fusion, during which a lipidic fusion pore develops in a local and transient hemifusion diaphragm. PMID:9508770

Whole cell homogenates of Naegleria fowleri were examined by hemolytic and /sup 51/Cr-release assays for the presence of cytolytic molecules which may participate in the cytopathogenic action of this amoeba. Two distinct cytolytic activities were found. A surface membrane cytolysin was identified which was found to be avidly associated with membranes possessing an equilibrium density of 1.135 g/cm/sup 3/ in isopycnic sucrose gradients. The activity of the surface membrane cytolysin was not affected by heating at 75/sup 0/C for 30 min. The second cytolytic activity was found in putative lysosomes possessing an equilibrium density of 1.162 g/cm/sup 3/ and was completely inactivated by heating at 75/sup 0/C for 30 min. Cytolysis produced in the presence of both cytolysins was consistently synergistic with respect to the activity of either cytolysin alone. The lesions produced on erythrocytes by this cooperative process were characterized by electron microscopy as transmembrane pores resembling a number of other cytolytic effector molecules including the ninth component of complement, perforins of cytolytic T lymphocytes, and the alphatoxin of Staphylococcus aureus.

Naturally occurring and contaminant ferromagnetic and ferrimagnetic particles have been found within or near cells, and might allow pulsed magnetic fields to create transient cell membrane opening ("pores"). We show that this possibility is significantly constrained by the maximum rotational energy that can be transferred to the cell membrane. For single biologically synthesized magnetosomes (radius rmag approximately 10(-7) m, magnetic moment mu approximately 2 x 10(-15) A m2) and typical cell membranes, the estimated pulse magnitude must exceed Bo approximately 6 x 10(-3) to 7 x 10(-2) T, and the optimal pulse durations are in the range 10(-5) s < tpulse < 10(-1) s. For larger contaminant particles with larger net magnetic moments, the pulse magnitudes could be only somewhat smaller, and the optimal durations are about the same. Very large pulses that exceed the coercive force of a particle are predicted to have a smaller effective magnitude and shorter effective duration. PMID:8842201

Canonical inflammasome activation induces a caspase-1/gasdermin D (Gsdmd)-dependent lytic cell death called pyroptosis that promotes antimicrobial host defense but may contribute to sepsis. The nature of the caspase-1-dependent change in plasma membrane (PM) permeability during pyroptotic progression remains incompletely defined. We assayed propidium(2+) (Pro(2+)) influx kinetics during NLRP3 or Pyrin inflammasome activation in murine bone marrow-derived macrophages (BMDMs) as an indicator of this PM permeabilization. BMDMs were characterized by rapid Pro(2+) influx after initiation of NLRP3 or Pyrin inflammasomes by nigericin (NG) or Clostridium difficile toxin B (TcdB), respectively. No Pro(2+) uptake in response to NG or TcdB was observed in Casp1(-/-) or Asc(-/-) BMDMs. The cytoprotectant glycine profoundly suppressed NG and TcdB-induced lysis but not Pro(2+) influx. The absence of Gsdmd expression resulted in suppression of NG-stimulated Pro(2+) influx and pyroptotic lysis. Extracellular La(3+) and Gd(3+) rapidly and reversibly blocked the induced Pro(2+) influx and markedly delayed pyroptotic lysis without limiting upstream inflammasome assembly and caspase-1 activation. Thus, caspase-1-driven pyroptosis requires induction of initial prelytic pores in the PM that are dependent on Gsdmd expression. These PM pores also facilitated the efflux of cytosolic ATP and influx of extracellular Ca(2+) Although lanthanides and Gsdmd deletion both suppressed PM pore activity and pyroptotic lysis, robust IL-1β release was observed in lanthanide-treated BMDMs but not in Gsdmd-deficient cells. This suggests roles for Gsdmd in both passive IL-1β release secondary to pyroptotic lysis and in nonlytic/nonclassical IL-1β export. PMID:27385778

Porous poly(arylene ether ketone) (PAEK) membranes are prepared by selective removal of poly(lactic acid) (PLA) molecules from self-assembled PAEK-PLA block copolymers. The pore size and porosity of the membranes are precisely controlled by adjusting PLA concentration. The synthesis of the PAEK-PLA copolymer is confirmed by FTIR and NMR spectroscopies and the morphology of the membrane is examined by scanning electron microscopy (SEM). Several important properties such as liquid electrolyte uptake, contact angle, thermal and mechanical stability, and lithium ion conductivity are measured and compared with those of commercial poly(propylene) (PP) membranes to investigate their application feasibility as a separator. The porous PAEK membrane shows improved thermal and dimensional stability compared to the PP membrane. The EC/DEC/EMC (1:1:1, v/v/v) soaked PAEK membrane with a pore diameter of 50 nm shows the highest lithium ion conductivity, higher than that of PP membrane. More importantly, the porous PAEK membranes show superior liquid electrolyte holding capacity to the PP membrane.

The physicochemical landscape of the bilayer modulates membrane protein function. Actinoporins are a family of potent hemolytic proteins from sea anemones acting at the membrane level. This family of cytolysins preferentially binds to target membranes containing sphingomyelin, where they form lytic pores giving rise to cell death. Although the cytolytic activity of the actinoporin fragaceatoxin C (FraC) is sensitive to vesicles made of various lipid compositions, it is far from clear how this toxin adjusts its mechanism of action to a broad range of physiochemical landscapes. Herein, we show that the conserved residue Phe-16 of FraC is critical for pore formation in cholesterol-rich membranes such as those of red blood cells. The interaction of a panel of muteins of Phe-16 with model membranes composed of raft-like lipid domains is inactivated in cholesterol-rich membranes but not in cholesterol-depleted membranes. These results indicate that actinoporins recognize different membrane environments, resulting in a wider repertoire of susceptible target membranes (and preys) for sea anemones. In addition, this study has unveiled promising candidates for the development of protein-based biosensors highly sensitive to the concentration of cholesterol within the membrane. PMID:25759390

The physicochemical landscape of the bilayer modulates membrane protein function. Actinoporins are a family of potent hemolytic proteins from sea anemones acting at the membrane level. This family of cytolysins preferentially binds to target membranes containing sphingomyelin, where they form lytic pores giving rise to cell death. Although the cytolytic activity of the actinoporin fragaceatoxin C (FraC) is sensitive to vesicles made of various lipid compositions, it is far from clear how this toxin adjusts its mechanism of action to a broad range of physiochemical landscapes. Herein, we show that the conserved residue Phe-16 of FraC is critical for pore formation in cholesterol-rich membranes such as those of red blood cells. The interaction of a panel of muteins of Phe-16 with model membranes composed of raft-like lipid domains is inactivated in cholesterol-rich membranes but not in cholesterol-depleted membranes. These results indicate that actinoporins recognize different membrane environments, resulting in a wider repertoire of susceptible target membranes (and preys) for sea anemones. In addition, this study has unveiled promising candidates for the development of protein-based biosensors highly sensitive to the concentration of cholesterol within the membrane. PMID:25759390

Semipermeable membrane devices (SPMDs) were employed to sample sediment pore water in static exposure studies under controlled laboratory conditions using (control pond and formulated) sediments fortified with 15 priority pollutant polycyclic aromatic hydrocarbons (PPPAHs). The sediment fortification level of 750 ng/g was selected on the basis of what might be detected in a sediment sample from a contaminated area. The sampling interval consisted of 0, 4, 7, 14, and 28 days for each study. The analytical methodologies, as well as the extraction and sample cleanup procedures used in the isolation, characterization, and quantitation of 15 PPPAHs at different fortification levels in SPMDs, water, and sediment were reported previously (Williamson, M.S. Thesis, University of Missouri-Columbia, USA; Williamson et al., Chemosphere (This issue--PII: S0045-6535(02)00394-6)) and used for this project. Average (mean) extraction recoveries for each PPPAH congener in each matrix are reported and discussed. No procedural blank extracts (controls) were found to contain any PPPAH residues above the method quantitation limit, therefore, no matrix interferences were detected. The focus of this publication is to demonstrate the ability to sequester environmental contaminants, specifically PPPAHs, from sediment pore water using SPMDs and two different types of fortified sediment. PMID:12431008

Porous alumina membranes (PAMs) were fabricated using a two-step oxidization method in oxalic acid. Polycrystalline PAMs have been prepared after annealing at different temperatures. The high-temperature properties of the PAMs were investigated using scanning electron microscopy, thermal analysis, X-ray diffraction and infrared spectrometer. At 870°C the amorphous alumina crystallizes to γ-Al2O3. Finally at 1228°C the alumina converts into the thermodynamically preferred phase, α-Al2O3. Differential thermal analysis showed that there was a gradual weight loss at about 900°C due to decomposed of oxalate. A mass of carboxylate ions and carboxylic groups were found in the infrared spectrum of PAMs, and reduced with the increasing of annealing temperature. Characteristic analysis with scanning electron microscopy shows that the pore structure of the PAMs was very stable and there was no detectable structural modification below 900°C, and microstructures of the pores changed slightly during the transformation from α-Al2O3 to γ-Al2O3 while increasing the annealing temperature.

Micro- and nanoporous systems incorporating bioactive molecules, such as enzymes, are very promising supports for biocatalysis. Here, we investigate the influence of geometrical confinement on the layer-by-layer (LbL) assembly of enzyme-based thin films, using the polyionic couple (chitosan/β-lactamase)n. Thin films with different number of layers were prepared on flat silicon wafers and within cylindrical submicron pores of polycarbonate membranes to determine the impact of the confinement of macromolecules on: (i) the LbL film growth, (ii) the enzyme loading, and (iii) the biocatalytic efficiency. Solid-state NMR is employed to estimate the amount of enzyme loaded in the different types of LbL films, and the enzyme activity is determined by the study of the kinetics of nitrocefin hydrolysis. Film growth and loading of enzyme occur faster in the confined medium, until pores reach saturation. Moreover, when LbL films are grown within nanopores, the weight fraction of enzyme is very high and remains constant along the build-up. Conversely, the relative amount of enzyme in flat films significantly decreases with the number of layers due to the partial exchange during the growth. Finally, our study emphasizes that the immobilization of enzymes through LbL assembly in confined media can lead to very active surfaces with a restricted number of LbL cycles.

Translocation of nuclear-encoded preproteins across the outer membrane of mitochondria is mediated by the multicomponent transmembrane TOM complex. We have isolated the TOM core complex of Neurospora crassa by removing the receptors Tom70 and Tom20 from the isolated TOM holo complex by treatment with the detergent dodecyl maltoside. It consists of Tom40, Tom22, and the small Tom components, Tom6 and Tom7. This core complex was also purified directly from mitochondria after solubilization with dodecyl maltoside. The TOM core complex has the characteristics of the general insertion pore; it contains high-conductance channels and binds preprotein in a targeting sequence-dependent manner. It forms a double ring structure that, in contrast to the holo complex, lacks the third density seen in the latter particles. Three-dimensional reconstruction by electron tomography exhibits two open pores traversing the complex with a diameter of approximately 2.1 nm and a height of approximately 7 nm. Tom40 is the key structural element of the TOM core complex. PMID:10579717

Semipermeable membrane devices (SPMDs) were employed to sample sediment pore water in static exposure studies under controlled laboratory conditions using (control pond and formulated) sediments fortified with 15 priority pollutant polycyclic aromatic hydrocarbons (PPPAHs). The sediment fortification level of 750 ng/g was selected on the basis of what might be detected in a sediment sample from a contaminated area. The sampling interval consisted of 0, 4, 7, 14, and 28 days for each study. The analytical methodologies, as well as the extraction and sample cleanup procedures used in the isolation, characterization, and quantitation of 15 PPPAHs at different fortification levels in SPMDs, water, and sediment were reported previously (Williamson, M.S. Thesis, University of Missouri - Columbia, USA; Williamson et al., Chemosphere (This issue - PII: S0045-6535(02)00394-6)) and used for this project. Average (mean) extraction recoveries for each PPPAH congener in each matrix are reported and discussed. No procedural blank extracts (controls) were found to contain any PPPAH residues above the method quantitation limit, therefore, no matrix interferences were detected. The focus of this publication is to demonstrate the ability to sequester environmental contaminants, specifically PPPAHs, from sediment pore water using SPMDs and two different types of fortified sediment.

We recently reported that the glutathione transferase in rat liver mitochondrial membranes (mtMGST1) is activated by S-glutathionylation and the activated mtMGST1 contributes to the mitochondrial permeability transition (MPT) pore and cytochrome c release from mitochondria [Lee, K.K., Shimoji, M., Quazi, S.H., Sunakawa, H., Aniya, Y., 2008. Novel function of glutathione transferase in rat liver mitochondrial membrane: role for cytochrome c release from mitochondria. Toxcol. Appl. Pharmacol. 232, 109-118]. In the present study we investigated the effect of reactive oxygen species (ROS), generator gallic acid (GA) and GST inhibitors on mtMGST1 and the MPT. When rat liver mitochondria were incubated with GA, mtMGST1 activity was increased to about 3 fold and the increase was inhibited with antioxidant enzymes and singlet oxygen quenchers including 1,4-diazabicyclo [2,2,2] octane (DABCO). GA-mediated mtMGST1 activation was prevented by GST inhibitors such as tannic acid, hematin, and cibacron blue and also by cyclosporin A (CsA). In addition, GA induced the mitochondrial swelling which was also inhibited by GST inhibitors, but not by MPT inhibitors CsA, ADP, and bongkrekic acid. GA also released cytochrome c from the mitochondria which was inhibited completely by DABCO, moderately by GST inhibitors, and somewhat by CsA. Ca{sup 2+}-mediated mitochondrial swelling and cytochrome c release were inhibited by MPT inhibitors but not by GST inhibitors. When the outer mitochondrial membrane was isolated after treatment of mitochondria with GA, mtMGST1 activity was markedly increased and oligomer/aggregate of mtMGST1 was observed. These results indicate that mtMGST1 in the outer mitochondrial membrane is activated by GA through thiol oxidation leading to protein oligomerization/aggregation, which may contribute to the formation of ROS-mediated, CsA-insensitive MPT pore, suggesting a novel mechanism for regulation of the MPT by mtMGST1.

Robust filtering techniques capable of efficiently removing particulates and biological agents from water or air suffer from plugging, poor rejuvenation, low permeance, and high backpressure. Operational characteristics of pressure-driven separations are in part controlled by the membranepore size, charge of particulates, transmembrane pressure and the requirement for sufficient water flux to overcome fouling. With long term use filters decline in permeance due to filter-cake plugging of pores, fouling, or filter deterioration. Though metallic filter tube development at ORNL has focused almost exclusively on gas separations, a small study examined the applicability of these membranes for tangential filtering of aqueous suspensions of bacterial-sized particles. A mixture of fluorescent polystyrene microspheres ranging in size from 0.5 to 6 {micro}m in diameter simulated microorganisms in filtration studies. Compared to a commercial filter, the ORNL 0.6 {micro}m filter averaged approximately 10-fold greater filtration efficiency of the small particles, several-fold greater permeance after considerable use and it returned to approximately 85% of the initial flow upon backflushing versus 30% for the commercial filter. After filtering several liters of the particle-containing suspension, the ORNL composite filter still exhibited greater than 50% of its initial permeance while the commercial filter had decreased to less than 20%. When considering a greater filtration efficiency, greater permeance per unit mass, greater percentage of rejuvenation upon backflushing (up to 3-fold), and likely greater performance with extended use, the ORNL 0.6 {micro}m filters can potentially outperform the commercial filter by factors of 100-1000 fold.

There is increasing demand to functionalize meso- and nanoporous materials by coating and make the porous substrate biocompatible or environmentally friendly. However, coating on a meso-porous substrate poses great challenges, especially if the pore aspect ratio is high. We adopted the pulsed laser deposition (PLD) method to coat Ni(3)Al-based meso-porous membranes, which were fabricated from a single-crystal Ni-based superalloy by a unique selective phase dissolution technique. These membranes were about 250 µm thick and had channel-like pores (∼200 nm wide) with very high aspect ratio. Two different coating materials, i.e. diamond-like carbon (DLC) and titanium, were used to coat these membranes. High energy C or Ti ions, produced in the plasma plume by the PLD process, penetrated the channel-like pores and deposited coatings on the pore walls deep inside the membrane. The thickness and the quality of coatings on the pore walls were examined using the dual-beam system. The coating thickness, of the order of 50 nm, was adherent to the pore walls and was quite uniform at different depths. The carbon and the Ti deposition behaved quite similarly. The preliminary experiments showed that the PLD is an adequate method for coating fine open cavities of complex geometry. Simulations based on stopping and the range of ions in matter (SRIM) calculations helped in understanding the deposition processes on pore walls at great depths. PMID:21730712

We have applied a combined fluorescence microscopy and single-ion-channel electric current recording approach, correlating with molecular dynamics (MD) simulations, to study the mechanism of voltage-sensor domain translocation across a lipid bilayer. We use the colicin Ia ion channel as a model system, and our experimental and simulation results show the following: (1) The open-close activity of an activated colicin Ia is not necessarily sensitive to the amplitude of the applied cross-membrane voltage when the cross-membrane voltage is around the resting potential of excitable membranes; and (2) there is a significant probability that the activation of colicin Ia occurs by forming a transient and fluctuating water pore of ˜15 Å diameter in the lipid bilayer membrane. The location of the water-pore formation is nonrandom and highly specific, right at the insertion site of colicin Ia charged residues in the lipid bilayer membrane, and the formation is intrinsically associated with the polypeptide conformational fluctuations and solvation dynamics. Our results suggest an interesting mechanistic pathway for voltage-sensitive ion channel activation, and specifically for translocation of charged polypeptide chains across the lipid membrane under a transmembrane electric field: the charged polypeptide domain facilitates the formation of hydrophilic water pore in the membrane and diffuses through the hydrophilic pathway across the membrane; i.e., the charged polypeptide chain can cross a lipid membrane without entering into the hydrophobic core of the lipid membrane but entirely through the aqueous and hydrophilic environment to achieve a cross-membrane translocation. This mechanism sheds light on the intensive and fundamental debate on how a hydrophilic and charged peptide domain diffuses across the biologically inaccessible high-energy barrier of the hydrophobic core of a lipid bilayer: The peptide domain does not need to cross the hydrophobic core to move across a

Actinoporin equinatoxin II (EqtII) is an archetypal example of α-helical pore-forming toxins that porate cellular membranes by the use of α-helices. Previous studies proposed several steps in the pore formation: binding of monomeric protein onto the membrane, followed by oligomerization and insertion of the N-terminal α-helix into the lipid bilayer. We studied these separate steps with an EqtII triple cysteine mutant. The mutant was engineered to monitor the insertion of the N terminus into the lipid bilayer by labeling Cys-18 with a fluorescence probe and at the same time to control the flexibility of the N-terminal region by the disulfide bond formed between cysteines introduced at positions 8 and 69. The insertion of the N terminus into the membrane proceeded shortly after the toxin binding and was followed by oligomerization. The oxidized, non-lytic, form of the mutant was still able to bind to membranes and oligomerize at the same level as the wild-type or the reduced form. However, the kinetics of the N-terminal helix insertion, the release of calcein from erythrocyte ghosts, and hemolysis of erythrocytes was much slower when membrane-bound oxidized mutant was reduced by the addition of the reductant. Results show that the N-terminal region needs to be inserted in the lipid membrane before the oligomerization into the final pore and imply that there is no need for a stable prepore formation. This is different from β-pore-forming toxins that often form β-barrel pores via a stable prepore complex. PMID:23803608

Abstract Recent molecular-dynamics simulations have suggested that the arginine-rich HIV Tat peptides translocate by destabilizing and inducing transient pores in phospholipid bilayers. In this pathway for peptide translocation, Arg residues play a fundamental role not only in the binding of the peptide to the surface of the membrane, but also in the destabilization and nucleation of transient pores across the bilayer. Here we present a molecular-dynamics simulation of a peptide composed of nine Args (Arg-9) that shows that this peptide follows the same translocation pathway previously found for the Tat peptide. We test experimentally the hypothesis that transient pores open by measuring ionic currents across phospholipid bilayers and cell membranes through the pores induced by Arg-9 peptides. We find that Arg-9 peptides, in the presence of an electrostatic potential gradient, induce ionic currents across planar phospholipid bilayers, as well as in cultured osteosarcoma cells and human smooth muscle cells. Our results suggest that the mechanism of action of Arg-9 peptides involves the creation of transient pores in lipid bilayers and cell membranes. PMID:19804722

Recent molecular-dynamics simulations have suggested that the arginine-rich HIV Tat peptides translocate by destabilizing and inducing transient pores in phospholipid bilayers. In this pathway for peptide translocation, Arg residues play a fundamental role not only in the binding of the peptide to the surface of the membrane, but also in the destabilization and nucleation of transient pores across the bilayer. Here we present a molecular-dynamics simulation of a peptide composed of nine Args (Arg-9) that shows that this peptide follows the same translocation pathway previously found for the Tat peptide. We test experimentally the hypothesis that transient pores open by measuring ionic currents across phospholipid bilayers and cell membranes through the pores induced by Arg-9 peptides. We find that Arg-9 peptides, in the presence of an electrostatic potential gradient, induce ionic currents across planar phospholipid bilayers, as well as in cultured osteosarcoma cells and human smooth muscle cells. Our results suggest that the mechanism of action of Arg-9 peptides involves the creation of transient pores in lipid bilayers and cell membranes. PMID:19804722

Lysosomal calcium (Ca2+) release mediated by NAADP triggers signalling cascades that regulate many cellular processes. The identification of two-pore channel 2 (TPC2) as the NAADP receptor advances our understanding of lysosomal Ca2+ signalling, yet the lysosome is not amenable to traditional patch-clamp electrophysiology. Previous attempts to record TPC2 single-channel activity put TPC2 outside its native environment, which not reflect TPC2’s true physiological properties. To test the feasibility of using nuclear membrane electrophysiology for TPC2 channel characterization, we constructed a stable human TPC2-expressing DT40TKO cell line that lacks endogenous InsP3R and RyR (DT40TKO-hTPC2). Immunostaining revealed hTPC2 expression on the ER and nuclear envelope. Intracellular dialysis of NAADP into Fura-2-loaded DT40TKO-hTPC2 cells elicited cytosolic Ca2+ transients, suggesting that hTPC2 was functionally active. Using nuclear membrane electrophysiology, we detected a ~220 pS single-channel current activated by NAADP with K+ as the permeant ion. The detected single-channel recordings displayed a linear current-voltage relationship, were sensitive to Ned-19 inhibition, were biphasically regulated by NAADP concentration, and regulated by PKA phosphorylation. In summary, we developed a cell model for the characterization of the TPC2 channel and the nuclear membrane patch-clamp technique provided an alternative approach to rigorously investigate the electrophysiological properties of TPC2 with minimal manipulation. PMID:26838264

Lysosomal calcium (Ca(2+)) release mediated by NAADP triggers signalling cascades that regulate many cellular processes. The identification of two-pore channel 2 (TPC2) as the NAADP receptor advances our understanding of lysosomal Ca(2+) signalling, yet the lysosome is not amenable to traditional patch-clamp electrophysiology. Previous attempts to record TPC2 single-channel activity put TPC2 outside its native environment, which not reflect TPC2's true physiological properties. To test the feasibility of using nuclear membrane electrophysiology for TPC2 channel characterization, we constructed a stable human TPC2-expressing DT40TKO cell line that lacks endogenous InsP3R and RyR (DT40TKO-hTPC2). Immunostaining revealed hTPC2 expression on the ER and nuclear envelope. Intracellular dialysis of NAADP into Fura-2-loaded DT40TKO-hTPC2 cells elicited cytosolic Ca(2+) transients, suggesting that hTPC2 was functionally active. Using nuclear membrane electrophysiology, we detected a ~220 pS single-channel current activated by NAADP with K(+) as the permeant ion. The detected single-channel recordings displayed a linear current-voltage relationship, were sensitive to Ned-19 inhibition, were biphasically regulated by NAADP concentration, and regulated by PKA phosphorylation. In summary, we developed a cell model for the characterization of the TPC2 channel and the nuclear membrane patch-clamp technique provided an alternative approach to rigorously investigate the electrophysiological properties of TPC2 with minimal manipulation. PMID:26838264

The recent high-resolution structure of the toxin FraC derived from the sea anemone Actinia fragacea has provided new insight into the mechanism of pore formation by actinoporins. In this work, we report two new crystal forms of FraC in its oligomeric prepore conformation. Together with the previously reported structure, these two new structures reveal that ring-like nonamers of the toxin assemble into compact two-dimensional hexagonal arrays. This supramolecular organization is maintained in different relative orientations adopted by the oligomers within the crystal layers. Analyses of the aggregation of FraC pores in both planar and curved (vesicles) model membranes show similar 2D hexagonal arrangements. Our observations support a model in which hexagonal pore-packing is a clustering mechanism that maximizes toxin-driven membrane damage in the target cell. PMID:22728830

Voltage-gated K+ channels underlie the electrical excitability of cells. Each subunit of the functional tetramer consists of the tandem fusion of two modules, an N-terminal voltage-sensor and a C-terminal pore. To investigate how sensor coupling to the pore generates voltage-dependent channel opening, we solved the crystal structure and characterized the function of a voltage-gated K+ channel pore in a lipid membrane. The structure of a functional channel in a membrane environment at 3.1 Å resolution establishes an unprecedented connection between channel structure and function. The structure is unique in delineating an ion-occupied ready to conduct selectivity filter, a confined aqueous cavity, and a closed activation gate, embodying a dynamic entity trapped in an unstable closed state. PMID:23095758

Organic arsenic in waters has been a global concern in drinking water due to its higher toxicity to humans. In this study, a novel zirconium/polyvinyl alcohol (PVA) modified polyvinylidene fluoride (PVDF) membrane was applied to remove organic arsenic from water. The impregnation of zirconium ions within the modified membrane was attributed to the coordination reactions among the zirconium ions, ether and hydroxyl groups. The synthesized membrane worked better at the acidic conditions and achieved the optimal uptake for both monomethylarsonic (MMA) and dimethylarsinic (DMA) at pH 2.0. The adsorption isotherm study demonstrated that the adsorption of both organic arsenic species was controlled by the mono-layer adsorption process; the maximum adsorption capacities for MMA and DMA were 73.04 and 37.53mg/g at pH 2, and 29.78 and 19.03mg/g at pH 7.0, respectively. The presence of humic acid had a negligible impact on the uptake of organic arsenic, whereas varying impacts on the arsenic adsorption were observed due to the presence of coexisting anions such as fluoride, phosphate, carbonate and silicate. A single piece of membrane with a surface area of only 12.56cm(2) could treat 7.5-L MMA and 4.1-L DMA solution with an influent concentration of about 100μg/L to meet the WHO and USEPA standard of 10μg/L. Based on the XPS analyses, the ion exchange reaction between chloride ions on the membrane surface and organic arsenic species was responsible for the removal of both MMA and DMA. PMID:27267042

Resident integral proteins of the inner nuclear membrane (INM) are synthesized as membrane-integrated proteins on the peripheral endoplasmic reticulum (ER) and are transported to the INM throughout interphase using an unknown trafficking mechanism. To study this transport, we developed a live cell assay that measures the movement of transmembrane reporters from the ER to the INM by rapamycin-mediated trapping at the nuclear lamina. Reporter constructs with small (<30 kD) cytosolic and lumenal domains rapidly accumulated at the INM. However, increasing the size of either domain by 47 kD strongly inhibited movement. Reduced temperature and ATP depletion also inhibited movement, which is characteristic of membrane fusion mechanisms, but pharmacological inhibition of vesicular trafficking had no effect. Because reporter accumulation at the INM was inhibited by antibodies to the nuclear poremembrane protein gp210, our results support a model wherein transport of integral proteins to the INM involves lateral diffusion in the lipid bilayer around the nuclear poremembrane, coupled with active restructuring of the nuclear pore complex. PMID:15611332

The strength of track etched membranes and prepared on their base polymer/metal composites is analysed in point of view of the pores form evolution during the extension and the interaction of elastic mechanical fields on closely positioned pores. The stress-strain curves for track membranes and composites PET/Cu are demonstrated for pore density 1.2×107сm-2 and diameters from 0.06 μm to 2.9 μm

The field of block polymer-based membranes for separation applications has grown considerably in the past several years. However, decreasing the domain sizes of these membranes to below 5 nm has proven to be a challenge in many instances. Here, we demonstrate that a triblock polymer, polyisoprene- b-polystyrene- b-poly(tert-butyl methacrylate) (PI-PS-PtBMA), can be utilized to form nanoporous membranes capable of high flux and high selectivity based on both size and chemical composition. By controlling the synthesis, solution self-assembly, and non-solvent induced phase separation of these polymers, a scalable fabrication process can produce thin-film membranes that feature monodisperse pores approaching 1 nm in diameter, tunable pore-wall chemistry, good mechanical stability, and chlorine degradation resistance. The PtBMA functionality can further be converted to a number of side chain functionalities through simple coupling chemistry to produce membranes with specific chemical and structural characteristics tailored to meet the needs of various applications. In particular, these membranes provide a promising, inexpensive platform for chlorine degradation and fouling-resistant membranes for water purification that can be produced on an industrial scale.

Stochastic electrophoretic capture of individual nanometer-scale particles at the small opening of a conically shaped nanopore in a synthetic membrane is described. Particle capture is sensed using a scanning electrochemical microscope (SECM) to measure the decrease in the transport rate of a redox-active molecule through the pore. The SECM tip is positioned at the larger backside opening of pore and used to amperometrically monitor the transport rate prior, during, and after particle capture. Following capture, the particle is released by electrophoretically driving it out of the pore opening and back into the solution. The capture and release method is demonstrated by detection of charged polystyrene spheres (43-150-nm diameter) using a polycarbonate membrane with conically shaped pores, the small opening of the pore having a diameter of 60 nm. The inverse of the time to capture polystyrene spheres increases with particle concentration over the range 10(8)-10(10) particles/mL. Selective detection based on nanoparticle charge and size is also demonstrated. A quantitative theoretical description of the rate of particle capture is presented, and the physical mechanism of particle capture, based on the balance of electrostatic and entropic forces, is considered. PMID:15481960

As part of an effort to develop a peptide-based compound suitable for clinical use as a channel replacement therapeutic for treating channelopathies such as cystic fibrosis, we present a reductionist model that appears to grasp the characteristics of ion channeling peptides. In particular we present the observed changes in the functional characteristics of NK4-M2GlyR p22 (KKKKPARVGLGITTVLTMTTQS), a M2 GlyR derived channel forming peptide. Starting with a structure determined by multidimensional NMR (800 MHz) in SDS, a potential from CHARMM force-field was used to relax the structure of NK4-M2GlyR p22. Following the relaxation, numerous pore structures were generated for the symmetric five-helix assembly with geometries varying from cylindrical to conical. As it is difficult a priori to assign accurately the orientation of the hydrophilic portion of M2GlyR derived amphipath towards the inside of the pore, we tilted and rotated the helical structure by five different angles about the backbone axis before forming the pore. Energy minimization of the channel was performed in vacuum, in phosphotidylcholine (POPC) membrane, and 60% POPC 30% phosphotidylethanolamine (POPE) in order to determine the effect of the environment surrounding on the structure on its energy minimization. We will present the various pore assemblies, in the different membrane environments, used to predict the most probably membrane bound structure.

Two-pore channels (TPCs) are ancient members of the voltage-gated ion channel superfamily that localize to acidic organelles such as lysosomes. The TPC complex is the proposed target of the Ca2 +-mobilizing messenger NAADP, which releases Ca2 + from these acidic Ca2 + stores. Whereas details of TPC activation and native ion permeation remain unclear, a consensus has emerged around their function in regulating endolysosomal trafficking. This role is supported by recent proteomic data showing that TPCs interact with proteins controlling membrane organization and dynamics, including Rab GTPases and components of the fusion apparatus. Regulation of TPCs by PtdIns(3,5)P2 and/or NAADP (nicotinic acid adenine dinucleotide phosphate) together with their functional and physical association with Rab proteins provides a mechanism for coupling phosphoinositide and trafficking protein cues to local ion fluxes. Therefore, TPCs work at the regulatory cross-roads of (patho)physiological cues to co-ordinate and potentially deregulate traffic flow through the endolysosomal network. This review focuses on the native role of TPCs in trafficking and their emerging contributions to endolysosomal trafficking dysfunction. PMID:26009187

The structure of ultrathin cellulose acetate membranes, known as active layer membranes, has been investigated using small-angle neutron scattering. These membranes are known to have structural and functional similarity to the surface or skin layer in commercial reverse-osmosis (RO) membranes and hence are useful model systems for understanding the structure of the RO membrane skin layer. Active layer membranes were studied after swelling them with either D[sub 2]O or CD[sub 3]OD. The results in both cases clearly indicated the presence of very small (10--20 [angstrom]) porous structures in the membrane. The presence of such pores has been a subject of long-standing controversy in this area. The data were analyzed using a modified Debye-Bueche analysis and the resultant membrane structure was seen to agree well with structural information from electron microscopic studies. Finally, a possible explanation for the differences in scattering observed between the D[sub 2]O swollen membranes and the CD[sub 3]OD swollen membranes has been presented.

Polyaniline (PANI) decorated commercial filtration membranes, such as stainless steel meshes (SSMs) with 5μm pore size and polyvinylidene fluoride (PVDF) membranes with 2-0.22μm pore sizes, were fabricated by a simple one-step dilute polymerization at low temperature. Lots of short PANI nanofibers were firmly and uniformly coated onto the membrane surfaces, forming rough micro- and nanoscale structures and leading to underwater superoleophobicity with low oil-adhesion characteristic. Furthermore, we systematically studied the effect of pore size and pressure difference on oil-water separation ability of the obtained membranes. It was found that the PANI-modified SSMs with 5μm pore size were suitable for the separation of non-surfactant emulsions with water fluxes of more than 1000Lm(-2)h(-1) under gravity only. The PANI-modified PVDFmembranes were used for the effective separation of surfactant-stabilized emulsions with water fluxes up to 3000Lm(-2)h(-1) for 2μm pore size under 0.1bar or 0.22μm pore size under 0.6bar. In addition, the superhydrophilic membranes with PANI coatings were demonstrated for high oil rejection, stable underwater superoleophobic properties after ultrasonic treatment and immersing in oils and various harsh conditions, and high and steady water permeation flux after several cycles. PMID:26809105

The objective of this study was to investigate how ceramic membranepore size and filtration temperature influence the protein fractionation of skim milk by cross flow microfiltration (MF). Microfiltration was performed at a uniform transmembrane pressure with constant permeate flux to a volume concentration factor of 2.5. Three different membranepore sizes, 0.05, 0.10, and 0.20µm, were used at a filtration temperature of 50°C. Furthermore, at pore size 0.10µm, 2 different filtration temperatures were investigated: 50 and 60°C. The transmission of proteins increased with increasing pore size, giving the permeate from MF with the 0.20-µm membrane a significantly higher concentration of native whey proteins compared with the permeates from the 0.05- and 0.10-µm membranes (0.50, 0.24, and 0.39%, respectively). Significant amounts of caseins permeated the 0.20-µm membrane (1.4%), giving a permeate with a whitish appearance and a casein distribution (αS2-CN: αS1-CN: κ-CN: β-CN) similar to that of skim milk. The 0.05- and 0.10-µm membranes were able to retain all caseins (only negligible amounts were detected). A permeate free from casein is beneficial in the production of native whey protein concentrates and in applications where transparency is an important functional characteristic. Microfiltration of skim milk at 50°C with the 0.10-µm membrane resulted in a permeate containing significantly more native whey proteins than the permeate from MF at 60°C. The more rapid increase in transmembrane pressure and the significantly lower concentration of caseins in the retentate at 60°C indicated that a higher concentration of caseins deposited on the membrane, and consequently reduced the native whey protein transmission. Optimal protein fractionation of skim milk into a casein-rich retentate and a permeate with native whey proteins were obtained by 0.10-µm MF at 50°C. PMID:27265169

The kinetics of porin incorporation into black lipid membranes (BLM) made of phosphatidylinositol (PI) or oxidized cholesterol (Ox Ch) were studied by means of alternating current; the set-up was able to acquire resistance and capacitance simultaneously by means of a mixed double-frequency approach at 1 Hz and 1 KHz, respectively. Conductance was dependent on the interaction between protein-forming pores and lipids. For PI membranes below a porin concentration of 12.54 ng/ml, there was no membrane conductivity, whereas at 200 ng/ml a steady-state value was reached. Different behavior was displayed by Ox Ch membranes, in which a concentration of 12.54 ng/ml was sufficient to reach a steady state. The incorporation kinetics when porin was added after membrane formation were sigmoidal. When porin was present in the medium before membrane formation, the kinetics were sigmoidal for PI membranes but became exponential for Ox Ch membranes. Furthermore, for BLM made of PI, the conductance-versus-porin concentration relationship is sigmoidal, with a Hill coefficient of 5.6 +/- 0.07, which is functional evidence corroborating the six-channel repeating units seen previously. For BLM made of Ox Ch, this relationship followed a binding isotherm curve with a Hill coefficient of 0.934 +/- 0.129. PMID:8842220

Numerous transport processes occur between the two mitochondrial (mt) membranes due to the diverse functions and metabolic processes of the mt organelle. The metabolite and ion transport through the mt outer membrane (OM) is widely assumed to be mediated by the porin pore, whereas in the mt inner membrane (IM) specific carriers are responsible for transport processes. Here, we provide evidence by means of Blue Native (BN)-PAGE analysis, co-immunoprecipitation, and tandem affinity purification that the two mt OM proteins Om14p and Om45p associate with the porin pore. Porin molecules seem to assemble independently to build the core unit. A subpopulation of these core units interacts with Om14p and Om45p. With preparative tandem affinity purification followed by MS analysis, we could identify interaction partners of this OM complex, which are mainly localized within the mt IM and function as carriers for diverse molecules. We propose a model for the role of the two OM proteins in addressing the porin pore to bind to specific channels in the mt IM to facilitate transport of metabolites. PMID:22461620

The aim of this study was to elucidate the mechanism of membrane insertion and the structural organization of pores formed by Bacillus thuringiensis δ -endotoxin. We determined the relative affinities for membranes of peptides corresponding to the seven helices that compose the toxin pore-forming domain, their modes of membrane interaction, their structures within membranes, and their orientations relative to the membrane normal. In addition, we used resonance energy transfer measurements of all possible combinatorial pairs of membrane-bound helices to map the network of interactions between helices in their membrane-bound state. The interaction of the helices with the bilayer membrane was also probed by a Monte Carlo simulation protocol to determine lowest-energy orientations. Our results are consistent with a situation in which helices α 4 and α 5 insert into the membrane as a helical hairpin in an antiparallel manner, while the other helices lie on the membrane surface like the ribs of an umbrella (the ``umbrella model''). Our results also support the suggestion that α 7 may serve as a binding sensor to initiate the structural rearrangement of the pore-forming domain.

Proper functioning of intracellular membranes is critical for many cellular processes. A key feature of membranes is their ability to adapt to changes in environmental conditions by adjusting their composition so as to maintain constant biophysical properties, including fluidity and flexibility. Similar changes in the biophysical properties of membranes likely occur when intracellular processes, such as vesicle formation and fusion, require dramatic changes in membrane curvature. Similar modifications must also be made when nuclear pore complexes (NPCs) are constructed within the existing nuclear membrane, as occurs during interphase in all eukaryotes. Here we report on the role of the essential nuclear envelope/endoplasmic reticulum (NE/ER) protein Brl1 in regulating the membrane composition of the NE/ER. We show that Brl1 and two other proteins characterized previously-Brr6, which is closely related to Brl1, and Apq12-function together and are required for lipid homeostasis. All three transmembrane proteins are localized to the NE and can be coprecipitated. As has been shown for mutations affecting Brr6 and Apq12, mutations in Brl1 lead to defects in lipid metabolism, increased sensitivity to drugs that inhibit enzymes involved in lipid synthesis, and strong genetic interactions with mutations affecting lipid metabolism. Mutations affecting Brl1 or Brr6 or the absence of Apq12 leads to hyperfluid membranes, because mutant cells are hypersensitive to agents that increase membrane fluidity. We suggest that the defects in nuclear pore complex biogenesis and mRNA export seen in these mutants are consequences of defects in maintaining the biophysical properties of the NE. PMID:26432634

Proper functioning of intracellular membranes is critical for many cellular processes. A key feature of membranes is their ability to adapt to changes in environmental conditions by adjusting their composition so as to maintain constant biophysical properties, including fluidity and flexibility. Similar changes in the biophysical properties of membranes likely occur when intracellular processes, such as vesicle formation and fusion, require dramatic changes in membrane curvature. Similar modifications must also be made when nuclear pore complexes (NPCs) are constructed within the existing nuclear membrane, as occurs during interphase in all eukaryotes. Here we report on the role of the essential nuclear envelope/endoplasmic reticulum (NE/ER) protein Brl1 in regulating the membrane composition of the NE/ER. We show that Brl1 and two other proteins characterized previously—Brr6, which is closely related to Brl1, and Apq12—function together and are required for lipid homeostasis. All three transmembrane proteins are localized to the NE and can be coprecipitated. As has been shown for mutations affecting Brr6 and Apq12, mutations in Brl1 lead to defects in lipid metabolism, increased sensitivity to drugs that inhibit enzymes involved in lipid synthesis, and strong genetic interactions with mutations affecting lipid metabolism. Mutations affecting Brl1 or Brr6 or the absence of Apq12 leads to hyperfluid membranes, because mutant cells are hypersensitive to agents that increase membrane fluidity. We suggest that the defects in nuclear pore complex biogenesis and mRNA export seen in these mutants are consequences of defects in maintaining the biophysical properties of the NE. PMID:26432634

Adequate mechanical strength is essential for materials used to reconstruct the orbital floor, and collagen membranes have recently been suggested for the repair of isolated fractures of the orbital floor. However, their mechanical properties after modification with pores for increased drainage of blood into the sinus have not been sufficiently investigated. We have tested the mechanical resistance of polydioxanone foils (PDS) to distortion and compared it with that of 3 resorbable collagen membranes (Smartbrane(®), Bio-Gide(®), and Creos(®)) in mint condition and when artificially aged (3 weeks, 6 weeks, and 8 weeks) after modification with pores (diameter 2mm) in a standard configuration (n=12 in each group). PDS and Creos(®) had comparable initial values for mechanical resistance of about 2.3N/mm(2), and Bio-Gide(®) and Smartbrane(®) had about 20% and 80% lower initial mechanical resistance, respectively. All materials tested had lower values after artificial ageing. After eight weeks of ageing, PDS lost about 99% of its initial mechanical resistance, Creos(®) about 66%, Bio-Gide(®) about 30%, and Smartbrane(®) about 95%. After 3 weeks the mechanical resistance in all groups was significantly less than the initial values (p=0.05), but there was no difference between samples aged artificially for 6 compared with 8 weeks. The mechanical resistance of the tested materials was not influenced by the presence of pores in a standard configuration and was in the appropriate range for moderate fractures of the orbital floor. We recommend further clinical investigations of collagen membranes modified with pores. PMID:26255542

Nanopores in arrays on silicon chips are functionalized with pH-responsive poly(methacrylic acid) (PMAA) brushes and used as supports for pore-spanning lipid bilayers with integrated membrane proteins. Robust platforms are created by the covalent grafting of polymer brushes using surface-initiated atom transfer radical polymerization (ATRP), resulting in sensor chips that can be successfully reused over several assays. His-tagged proteins are selectively and reversibly bound to the nitrilotriacetic acid (NTA) functionalization of the PMAA brush, and consequently lipid bilayer membranes are formed. The enhanced membrane resistance as determined by electrochemical impedance spectroscopy and free diffusion of dyed lipids observed as fluorescence recovery after photobleaching confirmed the presence of lipid bilayers. Immobilization of the His-tagged membrane proteins on the NTA-modified PMAA brush near the pore edges is characterized by fluorescence microscopy. This system allows us to adjust the protein density in free-standing bilayers, which are stabilized by the polymer brush underneath. The potential application of the integrated platform for ion channel protein assays is demonstrated.

Membrane operations are promising tools for efficient and environmentally friendly separations. However, the development of advanced membranes with tailored properties is a key issue to be addressed in order to better exploit the potentialities of membrane-based separations. An important approach toward this aim is the development of mixed matrix membranes in which an organic and an inorganic phase coexist in order to have synergic effects on membrane properties. The peculiar properties of carbon nanotubes (CNTs) such as high electrical and thermal conductivity, high strength and unique transport properties, has motivated a considerable effort to produce CNT-polymer composites in order to engineer membrane properties. In this work the roughness, wettability, morphology, crystalline phase and pore size of polyvinylidenefluoride (PVDF) membranes were tailored working on the membrane preparation conditions, as well as, by blending the polymer with multiwalled carbon nanotubes (MWCNTs). A study on the effect of concentration of the polymer, use of pore forming additives, type and concentration of MWCNTs (pristine and functionalized), was carried out. The results highlighted interesting relationships between membrane microstructure and composition, as well as, MWCNTs distribution, on transport and wettability properties, in the perspectives of a more efficient application of PVDFmembranes in liquid phase separations.

Tom40 is the main component of the preprotein translocase of the outer membrane of mitochondria (TOM complex). We have isolated Tom40 of Neurospora crassa by removing the receptor Tom22 and the small Tom components Tom6 and Tom7 from the purified TOM core complex. Tom40 is organized in a high molecular mass complex of approximately 350 kD. It forms a high conductance channel. Mitochondrial presequence peptides interact specifically with Tom40 reconstituted into planar lipid membranes and decrease the ion flow through the pores in a voltage-dependent manner. The secondary structure of Tom40 comprises approximately 31% beta-sheet, 22% alpha-helix, and 47% remaining structure as determined by circular dichroism measurements and Fourier transform infrared spectroscopy. Electron microscopy of purified Tom40 revealed particles primarily with one center of stain accumulation. They presumably represent an open pore with a diameter of approximately 2.5 nm, similar to the pores found in the TOM complex. Thus, Tom40 is the core element of the TOM translocase; it forms the protein-conducting channel in an oligomeric assembly. PMID:11402060

In this paper a 3-dimensional modeling of simultaneous stripping of carbon dioxide (CO2) and hydrogen sulfide (H2S) from water using hollow fiber membrane made of polyvinylidene fluoride is developed. The water, containing CO2 and H2S enters to the membrane as feed. At the same time, pure nitrogen flow in the shell side of a shell and tube hollow fiber as the solvent. In the previous methods of modeling hollow fiber membranes just one of the membranes was modeled and the results expand to whole shell and tube system. In this research the whole hollow fiber shell and tube module is modeled to reduce the errors. Simulation results showed that increasing the velocity of solvent flow and decreasing the velocity of the feed are leads to increase in the system yield. However the effect of the feed velocity on the process is likely more than the influence of changing the velocity of the gaseous solvent. In addition H2S stripping has higher yield in comparison with CO2 stripping. This model is compared to the previous modeling methods and shows that the new model is more accurate. Finally, the effect of feed temperature is studied using response surface method and the operating conditions of feed temperature, feed velocity, and solvent velocity is optimized according to synergistic effects. Simulation results show that, in the optimum operating conditions the removal percentage of H2S and CO2 are 27 and 21 % respectively.

In this paper a 3-dimensional modeling of simultaneous stripping of carbon dioxide (CO2) and hydrogen sulfide (H2S) from water using hollow fiber membrane made of polyvinylidene fluoride is developed. The water, containing CO2 and H2S enters to the membrane as feed. At the same time, pure nitrogen flow in the shell side of a shell and tube hollow fiber as the solvent. In the previous methods of modeling hollow fiber membranes just one of the membranes was modeled and the results expand to whole shell and tube system. In this research the whole hollow fiber shell and tube module is modeled to reduce the errors. Simulation results showed that increasing the velocity of solvent flow and decreasing the velocity of the feed are leads to increase in the system yield. However the effect of the feed velocity on the process is likely more than the influence of changing the velocity of the gaseous solvent. In addition H2S stripping has higher yield in comparison with CO2 stripping. This model is compared to the previous modeling methods and shows that the new model is more accurate. Finally, the effect of feed temperature is studied using response surface method and the operating conditions of feed temperature, feed velocity, and solvent velocity is optimized according to synergistic effects. Simulation results show that, in the optimum operating conditions the removal percentage of H2S and CO2 are 27 and 21 % respectively.

The practical application of membrane distillation (MD) for water purification is hindered by the absence of desirable membranes that can fulfill the special requirements of the MD process. Compared to the membranes fabricated by other methods, nanofiber membranes produced by electrospinning are of great interest due to their high porosity, low tortuosity, large surface pore size, and high surface hydrophobicity. However, the stable performance of the nanofiber membranes in the MD process is still unsatisfactory. Inspired by the unique structure of the lotus leaf, this study aimed to develop a strategy to construct superhydrophobic composite nanofiber membranes with robust superhydrophobicity and high porosity suitable for use in MD. The newly developed membrane consists of a superhydrophobic silica-PVDF composite selective skin formed on a polyvinylidene fluoride (PVDF) porous nanofiber scaffold via electrospinning. This fabrication method could be easily scaled up due to its simple preparation procedures. The effects of silica diameter and concentration on membrane contact angle, sliding angle, and MD performance were investigated thoroughly. For the first time, the direct contact membrane distillation (DCMD) tests demonstrate that the newly developed membranes are able to present stable high performance over 50 h of testing time, and the superhydrophobic selective layer exhibits excellent durability in ultrasonic treatment and a continuous DCMD test. It is believed that this novel design strategy has great potential for MD membrane fabrication. PMID:24797803

The cereal cell wall polysaccharide (1-3,1-4)-β-glucan is a linear polymer of glucose containing both β1-3 and β1-4 bonds. The structure of (1-3,1-4)-β-glucan varies between different cereals and during plant growth and development, but little is known about how this is controlled. The cellulose synthase–like CslF6 protein is an integral membrane protein and a major component of the (1-3,1-4)-β-glucan synthase. I show that a single amino acid within the predicted transmembrane pore domain of CslF6 controls (1-3,1-4)-β-glucan structure. A new mechanism for the control of the polysaccharide structure is proposed where membranepore architecture and the translocation of the growing polysaccharide across the membrane control how the acceptor glucan is coordinated at the active site and thus the proportion of β1-3 and β1-4 bonds within the polysaccharide. PMID:26601199

Theonellamides (TNMs) are antifungal and cytotoxic bicyclic dodecapeptides derived from the marine sponge Theonella sp. These peptides specifically bind to 3β-hydroxysterols, resulting in 1,3-β-D-glucan overproduction and membrane damage in yeasts. The inclusion of cholesterol or ergosterol in phosphatidylcholine membranes significantly enhanced the membrane affinity of theonellamide A (TNM-A) because of its direct interaction with 3β-hydroxyl groups of sterols. To better understand TNM-induced membrane alterations, we investigated the effects of TNM-A on liposome morphology. (31)P nuclear magnetic resonance (NMR) and dynamic light scattering (DLS) measurements revealed that the premixing of TNM-A with lipids induced smaller vesicle formation. When giant unilamellar vesicles were incubated with exogenously added TNM-A, confocal micrographs showed dynamic changes in membrane morphology, which were more frequently observed in cholesterol-containing than sterol-free liposomes. In conjunction with our previous data, these results suggest that the membrane action of TNM-A proceeds in two steps: 1) TNM-A binds to the membrane surface through direct interaction with sterols and 2) accumulated TNM-A modifies the local membrane curvature in a concentration-dependent manner, resulting in dramatic membrane morphological changes and membrane disruption. PMID:27003125

Pro-apoptotic Bax induces mitochondrial outer membrane permeabilization (MOMP) by forming oligomers through a largely undefined process. Using site-specific disulfide crosslinking, compartment-specific chemical labeling, and mutational analysis, we found that activated integral membrane Bax proteins form a BH3-in-groove dimer interface on the MOM surface similar to that observed in crystals. However, after the α5 helix was released into the MOM, the remaining interface with α2, α3, and α4 helices was rearranged. Another dimer interface was formed inside the MOM by two intersected or parallel α9 helices. Combinations of these interfaces generated oligomers in the MOM. Oligomerization was initiated by BH3-in-groove dimerization, without which neither the other dimerizations nor MOMP occurred. In contrast, α9 dimerization occurred downstream and was required for release of large but not small proteins from mitochondria. Moreover, the release of large proteins was facilitated by α9 insertion into the MOM and localization to the pore rim. Therefore, the BH3-in-groove dimerization on the MOM nucleates the assembly of an oligomeric Bax pore that is enlarged by α9 dimerization at the rim. PMID:26702098

Sticholysin I (St I) is a pore-forming toxin (PFT) produced by the Caribbean Sea anemone Stichodactyla helianthus belonging to the actinoporin protein family, a unique class of eukaryotic PFT. As for actinoporins, it has been proposed that the presence of cholesterol (Chol) and the coexistence of lipid phases increase binding to the target membrane and pore-forming ability. However, little is known about the role of membrane structure and dynamics (phase state, fluidity, and the presence of lipid domains) on the activity of actinoporins or which regions of the membrane are the most favorable for protein insertion, oligomerization, and eventually pore formation. To gain insight into the role of membrane properties on the functional activity of St I, we studied its binding to monolayers and vesicles of phosphatidylcholine (PC), sphingomyelin (SM), and sterols inducing (ergosterol -Erg and cholesterol -Chol) or not (cholestenone - Cln) membrane phase segregation in liquid ordered (Lo) and liquid disordered (Ld) domains. This study revealed that St I binds and permeabilizes with higher efficiency sterol-containing membranes independently of their ability to form domains. We discuss the results in terms of the relevance of different membrane properties for the actinoporins mechanism of action, namely, molecular heterogeneity, specially potentiated in membranes with sterols inducers of phase separation (Chol or Erg) or Cln, a sterol noninducer of phase separation but with a high propensity to induce nonlamellar phase. The role of the Ld phase is pointed out as the most suitable platform for pore formation. In this regard, such regions in Chol-containing membranes seem to be the most favored due to its increased fluidity; this property promotes toxin insertion, diffusion, and oligomerization leading to pore formation. PMID:26273899

We demonstrate the preparation and properties of poly(vinylidene fluoride) (PVDF) filtration membranes modified via surface zwitterionicalization mediated by reactive core-shell silica nanoparticles (SiO2 NPs). The organic/inorganic hybrid SiO2 NPs grafted with poly(methyl meth acrylate)-block-poly(2-dimethylaminoethyl methacrylate) copolymer (PMMA-b-PDMAEMA) shell were prepared by surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization and then used as a membrane-making additive of PVDFmembranes. The PDMAEMA exposed on membrane surface and pore walls were quaternized into zwitterionic poly(sulfobetaine methacrylate) (PSBMA) using 1,3-propane sultone (1,3-PS) as the quaternization agent. The membrane surface chemistry and morphology were analyzed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively. The hydrophilicity, permeability and antifouling ability of the investigated membranes were evaluated in detail. It was found that the PSBMA chains brought highly-hydrophilic and strong fouling resistant characteristics to PVDFmembranes due to the powerful hydration of zwitterionic surface. The SiO2 cores and PMMA chains in the hybrid NPs play a role of anchors for the linking of PSBMA chains to membrane surface. Compared to the traditional strategies for membrane hydrophilic modification, the developed method in this work combined the advantages of both blending and surface reaction. PMID:26835581

Polymer electrolyte membrane (PEM) fuel cells operate at levels of high humidity, leading to condensation throughout the cell components. The porous gas diffusion layer (GDL) must not become over-saturated with liquid water, due to its responsibility in providing diffusion pathways to and from the embedded catalyst sites. Due to the opaque and microscale nature of the GDL, a current challenge of the fuel cell industry is to identify the characteristics that make the GDL more or less robust against flooding. Modeling the system as a pore network is an attractive investigative strategy; however, for flooding simulations to provide meaningful material comparisons, accurate GDL topology and condensation distributions must be provided. The focus of this research is to provide the foundational tools with which to capture both of these requirements. The method of pore network modeling on topologically representative pore networks is demonstrated to describe flooding phenomena within GDL materials. A stochastic modeling algorithm is then developed to create pore spaces with the relevant features of GDL materials. Then, synchrotron based X-ray visualization experiments are developed and conducted to provide insight into condensation conditions. It was found that through-plane porosity distributions have significant effects on the GDL saturation levels. Some GDL manufacturing processes result in high porosity regions which are predicted to become heavily saturated with water if they are positioned between the condensation sites and the exhaust channels. Additionally, it was found that fiber diameter and the volume fraction of binding material applied to the GDL have significant impacts on the GDL heterogeneity and pore size distribution. Representative stochastic models must accurately describe these three material characteristics. In situ, dynamic liquid water behavior was visualized at the Canadian Light source, Inc. synchrotron using imaging and image processing

We demonstrate a nanoporous membrane device integrated with an on-chip microfluidic platform for the electrokinetic separation of biomolecules. This platform offers a thin (500 nm) film of anodized aluminum oxide directly fabricated and suspended onto a silicon substrate, assembled into a compact microfluidic device. We successfully showed the electrokinetic transport of ssDNA through the nano-porous membrane under various conditions. Size exclusive biomolecular separation driven by electric field was verified with the complex of thrombin and thrombin aptamer. This architecture enables an on-chip device for binary separation and size exclusive filtration targeted to various applications such as molecular detection and purification.

Proper balance of ions in intracellular and extracellular space is the key for normal cell functioning. Changes in the conductance of membranes for ions will lead to cell death. One of the main differences between normal and cancerous cells is the low extracellular pHe and the reverse pH gradient: intracellular pHi is higher than extracellular pHe. We report here pH-selective transfer of nano-pores to cancer cells for the dis-regulation of balance of monovalent cations to induce cell death at mildly acidic pHe as it is in most solid tumors. Our approach is based on the pH-sensitive fusion of cellular membrane with the liposomes containing gramicidin A forming cation-conductive β-helix in the membrane. Fusion is promoted only at low extracellular pH by the pH (Low) Insertion Peptide (pHLIP®) attached to the liposomes. Gramicidin channels inserted into the cancer cells open flux of protons into the cytoplasm and disrupt balance of other monovalent cations, which induces cell apoptosis.

To gain insight into mechanisms of photodynamic modification of biological membranes, we studied an impact of visible light in combination with a photosensitizer on translocation of various substances across artificial (vesicular and planar) bilayer lipid membranes (BLMs). Along with induction of carboxyfluorescein leakage from liposomes, pronounced stimulation of lipid flip-flop between the two monolayers was found after photosensitization, both processes being prevented by the singlet oxygen quencher sodium azide. On the contrary, no enhancement of potassium chloride efflux from liposomes was detected by conductometry under these conditions. Illumination of planar BLMs in the presence of a photosensitizer led to a marked increase in membrane permeability to amphiphilic 2-n-octylmalonic acid, but practically no change in the permeability to ammonia, which agreed with selective character of the photosensitized leakage of fluorescent dyes from liposomes (Pashkovskaya et al., Langmuir, 2010). Thus, the effect on transbilayer movement of molecules elicited by the photodynamic treatment substantially depended on the kind of translocated species, in particular, on their lipophilicity. Based on similarity with results of previous electroporation studies, we hypothesized about photodynamic induction of "pre-pores" or "hydrophobic defects" permeable to amphiphilic compounds and less permeable to hydrophilic substances and inorganic ions. PMID:21663731

The preparation of ion-track membranes of thermally stable poly( p-phenylene terephthalamide) (PPTA) was performed by ion beam irradiation followed by chemical etching with a sodium hypochlorite solution. Cylindrical pores were observed in the membrane irradiated with 197Au and 238U ions at an energy of 11.1 MeV/n. In contrast, funnel shape pores appeared in the membrane irradiated with 84Kr, 102Ru and 129Xe ion at energies of 6.2, 3.6 and 3.5 MeV/n, respectively. The 197Au and 238U ion irradiation was found to exhibit more than four times larger sensitivity to the track etching under the same etching conditions. Consequently, the pore shape can be controlled by the masses and energies of the irradiated ions, in close relation to the etching sensitivity of the track.

Fouling behaviours and antifouling properties of polyvinylidene fluoride (PVDF) ultrafiltration membranes blending with polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP) and polymethyl methacrylate (PMMA) had been investigated using the secondary effluent as the filtration medium. The results demonstrated that the antifouling properties of membranes using PVA and PVP as the additives were generally stronger than those using PMMA. Additives PVA and PVP could effectively improve the structural property and hydrophilicity of the membrane and result in an outstanding antifouling property. A dense membrane surface could prevent low molecular foulants from entering into the membranepores, depositing on the membrane with a loose spongy layer and penetrating into the internal macropore structure. The not fully generated internal macropores on the membrane surface were trend to be plugged, which resulted in serious flux decay and the membrane fouling was irreversible. Filtration cake formed on the membrane due to concentration polarization, which caused membrane flux decline and high flux recovery after cleaning. PMID:26370705

A novel protocol to generate and control porosity in polymeric structures is presented for fabrication of single ion polymer electrolyte (SIPE) membranes for lithium ion batteries. A series of SIPEs with varying ratios of aliphatic and aromatic segments was successfully synthesized and subsequently blended with PVDF-HFP to fabricate membranes of various sizes of pores. The membranes were characterized using techniques including SEM, solvent uptake capacity measurement and ionic conductivity. We demonstrate that appropriate membrane porosity enhances ionic conductivity, reduces interfacial resistance between electrodes and electrolyte and ultimately boosts performance of Li-ion batteries. The implication of the structure-performance relationship for battery design is discussed. PMID:25225970

The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4-30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores.

The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4-30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores. PMID:26592565

The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4–30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores. PMID:26592565

NAADP (nicotinic acid-adenine dinucleotide phosphate) is a potent Ca2+-mobilizing messenger implicated in many Ca2+-dependent cellular processes. It is highly unusual in that it appears to trigger Ca2+ release from acidic organelles such as lysosomes. These signals are often amplified by archetypal Ca2+ channels located in the endoplasmic reticulum. Recent studies have converged on the TPCs (two-pore channels) which localize to the endolysosomal system as the likely primary targets through which NAADP mediates its effects. 'Chatter' between TPCs and endoplasmic reticulum Ca2+ channels is disrupted when TPCs are directed away from the endolysosomal system. This suggests that intracellular Ca2+ release channels may be closely apposed, possibly at specific membrane contact sites between acidic organelles and the endoplasmic reticulum. PMID:22260682

We here report statistical analyses of 76 families of integral outer membranepore-forming proteins (OMPPs) found in bacteria and eukaryotic organelles. 47 of these families fall into one superfamily (SFI) which segregate into fifteen phylogenetic clusters. Families with members of the same protein size, topology and substrate specificities often cluster together. Virtually all OMPP families include only proteins that form transmembrane pores. Nine such families, all of which cluster together in the SFI phylogenetic tree, contain both α- and β-structures, are multi domain, multi subunit systems, and transport macromolecules. Most other SFI OMPPs transport small molecules. SFII and SFV homologues derive from Actinobacteria while SFIII and SFIV proteins derive from chloroplasts. Three families of actinobacterial OMPPs and two families of eukaryotic OMPPs apparently consist primarily of α-helices (α-TMSs). Of the 71 families of (putative) β-barrel OMPPs, only twenty could not be assigned to a superfamily, and these derived primarily from Actinobacteria (1), chloroplasts (1), spirochaetes (8), and proteobacteria (10). Proteins were identified in which two or three full length OMPPs are fused together. Family characteristic are described and evidence agrees with a previous proposal suggesting that many arose by adjacent β-hairpin structural unit duplications. PMID:27064789

In an effort to develop a peptide-based compound suitable for clinical use as a channel replacement therapeutic for treating channelopathies such as cystic fibrosis, we present a reductionist model that appears to capture many of the biophysical properties of an intact ion channel using short channel-forming peptides. We have developed two anion selective channel-forming peptides with near native and altered properties from the peptides derived from the glycine receptor: NK4-M2GlyR-p22 WT (KKKKPAR-VGLGITTVLTMTTQS) and NK4-M2GlyR-p22 S22W (KKKKPARVGLGITTVLTMTTQW), respectively. Starting with the two structures determined by solution multidimensional NMR (800 MHz) in SDS, we used CHARMM and NAMD to perform molecular dynamics simulations on the monomers. Using the existing experimental data, we then built an initial 5- helix assembly by altering the tilted angle, rotational angle and pore radius. We investigated the impact of the single mutation at position 22 on the structure and dynamics of the pore formed in a membrane build in a hydrated POPC lipid bilayer. Probable structures for both assemblies are presented.

Tailor-made polyvinylidene fluoride (PVDF) asymmetric hollow-fiber membranes and their membrane modules were employed for soluble gas removal, such as H{sub 2}S from waste gas streams. This study focused on the techniques of fabricating and characterizing the PVDF asymmetric hollow-fiber membranes and their membrane modules for removal of H{sub 2}S using an aqueous solution containing 10% NaOH. A laminar parabolic velocity profile was used to characterize the flow of the H{sub 2}S gas mixture in the hollow-fiber lumen. Effects of operating conditions and the morphological structures of the membranes on the membrane`s coefficient, k{sub AM}, were examined both theoretically and experimentally. The capabilities of the hollow-fiber membranes developed for removal of H{sub 2}S from waste gas streams were evaluated and compared with conventional symmetric hydrophobic hollow-fiber membranes, such as polypropylene. An analysis of H{sub 2}S transfer across the more developed PVDFmembranes reveals that the membrane`s coefficient, k{sub AM}, evaluated from its structure parameters, such as the effective surface porosity and mean radius, agreed well with the experimental data obtained from absorption experiments.

Hydrophilic poly(vinylidene fluoride) (PVDF) porous membranes are facilely fabricated via grafting polymerization and cross-linking reaction for vanadium flow battery (VFB) application. A solvent swelling pre-treatment is specifically carried out to introduce hydrophilic groups in the pores and on the surface, where they can form well connected ion transport networks. The modification is performed through chemical cross-linking and grafting of PVP by using potassium persulfate (K2S2O8) as a radical initiator. The effect of reaction condition on membrane morphology, hydrophilicity is characterized in detail. Meanwhile, the performance of modified membranes is detected in VFB single cell at a current density of 80 mA cm-2. It is found that more PVP is immobilized on membrane surface and in the pores with prolonging reaction time. Consequently, the membrane wetability and effective pore size change dramatically, resulting better hydrophilicity and higher ion selectivity. As a result, the VFBs assembled with these modified membranes show higher CE and overall better EE than unmodified ones. The optimized membrane shows CE of 94.4% and EE of 83.3%, which is comparable to commercial Nafion 115. Furthermore, the prepared hydrophilic PVDFmembranes demonstrate excellent chemical stability through the long-term battery operation, showing great prospects in VFB applications.

An aromatic polyamide membrane was used to study the separation of selected carboxylic acids, chlorophenols, nitrophenols and sodium chloride. An application for actual treatment of a coal-liquefaction waste water was also performed. Prediction of separation and flux data were obtained using the surface force pore flow (SFPF) model previously reported in the literature. Methods for the determination of pore size distribution of polyamide thin-film composite membrane and a cellulose acetate ultrafiltration membrane, solute concentration at the membrane wall are described. The pore distribution data and wall concentration data were further used with solute separation data at a particular pressure to obtain the solute-solvent-membrane wall forces parameter involved. From the knowledge of the interaction forces, the solute separation and flux data (for nonionized organic solutes and sodium chloride) were predicted over a wide range of pressures and showed excellent agreement with experimental data. The prediction of rejection and flux for carboxylic acids, chlorophenol and nitrophenol systems by the SFPF model were further extended to multicomponent systems. The polyamide membrane used in this study had 97-99% standard NaCl rejections and 24-30 gfd pure water flux at 20.7 x 10/sup 5/ N/m/sup 2/. For ionizable organics such as phenol, chlorophenol, dichlorophenol..., the rejection and flux drops were highly dependent on operating pH values. Membranes experimental results showed 99.5-99.8% rejection at pH 11 of phenol, 2-CP and 2,4-DCP. Under no ionization conditions the flux drop observed for nitrophenol and chlorophenol systems was not caused by osmotic pressure effect and was related to physicochemical nature of the solute-solvent-membrane system.

Separating molecular species is an important precursor for various applications. In this work, we have utilized molecular dynamics (MD) simulations to examine how pore radius and structure affect the separation process. We show from MD simulations that 2-D graphene sheets with designed sub-nanometer pores can efficiently separate the Kr-85 radionuclide gas from an N2/O2 mixture. Three species of gases (Kr-85, N2 and O2 were considered in the simulation box in which different sizes and geometries of pores were modeled on the graphene sheet. The ( 30× 30× 80 Å^3 simulation box contains a nanoporous graphene membrane in the middle of the box and two fixed walls with equal distances on both sides of the nanoporous graphene. The results revealed that Kr-85 separation was improved by using an optimized pore structure. It was also found that the Kr-85 gas radionuclides could be completely separated from nitrogen and oxygen molecules in the pore-7 configuration. Restriction of the molecular orientation largely prohibited the permeation of nitrogen molecules. It was also found that nitrogen was more strongly adsorbed onto the membrane than oxygen, while krypton was not adsorbed.

α-Pore-forming toxins (α-PFTs) are ubiquitous defense tools that kill cells by opening pores in the target cell membrane. Despite their relevance in host/pathogen interactions, very little is known about the pore stoichiometry and assembly pathway leading to membrane permeabilization. Equinatoxin II (EqtII) is a model α-PFT from sea anemone that oligomerizes and forms pores in sphingomyelin-containing membranes. Here, we determined the spatiotemporal organization of EqtII in living cells by single molecule imaging. Surprisingly, we found that on the cell surface EqtII did not organize into a unique oligomeric form. Instead, it existed as a mixture of oligomeric species mostly including monomers, dimers, tetramers, and hexamers. Mathematical modeling based on our data supported a new model in which toxin clustering happened in seconds and proceeded via condensation of EqtII dimer units formed upon monomer association. Furthermore, altering the pathway of EqtII assembly strongly affected its toxic activity, which highlights the relevance of the assembly mechanism on toxicity. PMID:25525270

α-Pore-forming toxins (α-PFTs) are ubiquitous defense tools that kill cells by opening pores in the target cell membrane. Despite their relevance in host/pathogen interactions, very little is known about the pore stoichiometry and assembly pathway leading to membrane permeabilization. Equinatoxin II (EqtII) is a model α-PFT from sea anemone that oligomerizes and forms pores in sphingomyelin-containing membranes. Here, we determined the spatiotemporal organization of EqtII in living cells by single molecule imaging. Surprisingly, we found that on the cell surface EqtII did not organize into a unique oligomeric form. Instead, it existed as a mixture of oligomeric species mostly including monomers, dimers, tetramers, and hexamers. Mathematical modeling based on our data supported a new model in which toxin clustering happened in seconds and proceeded via condensation of EqtII dimer units formed upon monomer association. Furthermore, altering the pathway of EqtII assembly strongly affected its toxic activity, which highlights the relevance of the assembly mechanism on toxicity. PMID:25525270

Anthrax toxin receptors act as molecular clamps or switches that control anthrax toxin entry, pH-dependent pore formation, and translocation of enzymatic moieties across the endosomal membranes. We previously reported that reduction of the disulfide bonds in the immunoglobulin-like (Ig) domain of the anthrax toxin receptor 2 (ANTXR2) inhibited the function of the protective antigen (PA) pore. In the present study, the disulfide linkage in the Ig domain was identified as Cys255-Cys279 and Cys230-Cys315. Specific disulfide bond deletion mutants were achieved by replacing Cys residues with Ala residues. Deletion of the disulfide bond C255-C279, but not C230-C315, inhibited the PA pore-induced release of the fluorescence dyes from the liposomes, suggesting that C255-C279 is essential for PA pore function. Furthermore, we found that deletion of C255-C279 did not affect PA prepore-to-pore conversion, but inhibited PA poremembrane insertion by trapping the PA membrane-inserting loops in proteinaceous hydrophobic pockets. Fluorescence spectra of Trp59, a residue adjacent to the PA-binding motif in von Willebrand factor A (VWA) domain of ANTXR2, showed that deletion of C255-C279 resulted in a significant conformational change on the receptor ectodomain. The disulfide deletion-induced conformational change on the VWA domain was further confirmed by single-particle 3D reconstruction of the negatively stained PA-receptor heptameric complexes. Together, the biochemical and structural data obtained in this study provides a mechanistic insight into the role of the receptor disulfide bond C255-C279 in anthrax toxin action. Manipulation of the redox states of the receptor, specifically targeting to C255-C279, may become a novel strategy to treat anthrax. PMID:26107617

We have elucidated a cost effective fabrication technique to produce superhydrophobic polyvinylidene fluoride (PVDF/DMF/candle soot particle and PVDF/DMF/camphor soot particle composite) porous materials. The water repellent dry composite was formed by the interaction of non-solvent (methanol) into PVDF/carbon soot particles suspension in N,N-dimethylformamide (DMF). It is seen that longer quenching time effectively changes the surface morphology of dry composites. The nano broccoli like hierarchical microstructure with micro or nano scaled roughen surface was obtained for PVDF/DMF/camphor soot particle, which reveals water contact angle of 172° with roll off angle of 2°. However, composite coating of PVDF/DMF/candle soot particle shows nano cauliflower like hierarchical, which illustrates water contact angle of 169° with roll off angle of 3°. To elucidate the enhancement of water repellent property of PVDF composites, we further divulge the evolution mechanism of nano cauliflower and nano broccoli structure. In order to evaluate the water contact angle of PVDF composites, surface diffusion of water inside the pores is investigated. Furthermore, the addition of small amount of carbon soot particles in composite not only provides the crystallization of PVDF, but also leads to dramatical amendment of surface morphology which increases the surface texture and roughness for superhydrophobicity. PMID:25268814

The mushroom Pleurotus ostreatus has been reported to produce the hemolytic proteins ostreolysin (OlyA), pleurotolysin A (PlyA) and pleurotolysin B (PlyB). The present study of the native and recombinant proteins dissects out their lipid-binding characteristics and their roles in lipid binding and membrane permeabilization. Using lipid-binding studies, permeabilization of erythrocytes, large unilamellar vesicles of various lipid compositions, and electron microscopy, we show that OlyA, a PlyA homolog, preferentially binds to membranes rich in sterol and sphingomyelin, but it does not permeabilize them. The N-terminally truncated Δ48PlyB corresponds to the mature and active form of native PlyB, and it has a membrane attack complex-perforin (MACPF) domain. Δ48PlyB spontaneously oligomerizes in solution, and binds weakly to various lipid membranes but is not able to perforate them. However, binding of Δ48PlyB to the cholesterol and sphingomyelin membranes, and consequently, their permeabilization is dramatically promoted in the presence of OlyA. On these membranes, Δ48PlyB and OlyA form predominantly 13-meric oligomers. These are rosette-like structures with a thickness of ∼9 nm from the membrane surface, with 19.7 nm and 4.9 nm outer and inner diameters, respectively. When present on opposing vesicle membranes, these oligomers can dimerize and thus promote aggregation of vesicles. Based on the structural and functional characteristics of Δ48PlyB, we suggest that it shares some features with MACPF/cholesterol-dependent cytolysin (CDC) proteins. OlyA is obligatory for the Δ48PlyB permeabilization of membranes rich in cholesterol and sphingomyelin. PMID:23806422

Macroporous chitosan/poly(vinyl alcohol) membrane adsorbents were synthesized by solvent evaporation in the presence of poly(ethylene glycol) which was utilized as porogen. The membranes were applied for Cu(II) ion adsorption from water. SEM, AFM and wettability analyses were performed for membrane characterization. Insertion of poly(ethylene glycol) generated macrovoids in the dense structure of CS/PVA membranes through particulate leaching out mechanism. According to the static adsorption tests, the uptake capacity of the porous membranes is elevated (˜26 mg/g) compared to that of the dense membranes (˜10 mg/g). This phenomenon is attributed to the increase in the density of active sites, water affinity and surface roughness as a result of the porogen effects. The approachability of the ions to the active sites was also affected by these important parameters. Both size and density of the macrovoids increased with increasing PEG content from nil to 5 wt%. Fragility of the resultant porous structures prohibited synthesizing CS/PVA membranes with higher porogen contents. Desorption tests showed that the porous membranes were better regenerated in comparison to the dense membranes using Na2EDTA as eluant. Generally, the results suggested that the CS/PVA membranes, comprising PEG as pore-generator agent, are potential candidates for adsorption and elimination of Cu(II) ions from water.

Ultraviolet (UV) filters represent a new class of micropollutants in water. To effectively remove these substances and minimize fouling during ultrafiltration, an electro-ultrafiltration process was used to separate benzophenone-3 (BP-3) from water by applying an electric field across the membrane. The effects of the electric field on the filtration performance, including resistance and retention, modification of polyvinylidene fluoride (PVDF) membrane and possible intermediates produced during electro-ultrafiltration, were studied thoroughly. The results clearly indicate that the combination of the electric field with ultrafiltration could increase BP-3 rejection and reduce filtration resistance. The membrane had a rougher surface and the pore size increased due to the modifications of PVDFmembrane induced by the electric field. The decrease in contact angle demonstrated the improvement of hydrophilicity in the PVDFmembrane surface after the electrofiltration treatment. The mechanism of BP-3 degradation in the electrofiltration was examined theoretically by calculating the frontier electron densities of the BP-3 molecule. The C3 atom in the BP-3 structure was demonstrated to be the most reactive site, which was consistent with the intermediate results identified by gas chromatography-mass spectrometry (GC-MS) analysis. PMID:23237763

Background Alamethicin is a membrane-active peptide isolated from the beneficial root-colonising fungus Trichoderma viride. This peptide can insert into membranes to form voltage-dependent pores. We have previously shown that alamethicin efficiently permeabilises the plasma membrane, mitochondria and plastids of cultured plant cells. In the present investigation, tobacco cells (Nicotiana tabacum L. cv Bright Yellow-2) were pre-treated with elicitors of defence responses to study whether this would affect permeabilisation. Results Oxygen consumption experiments showed that added cellulase, already upon a limited cell wall digestion, induced a cellular resistance to alamethicin permeabilisation. This effect could not be elicited by xylanase or bacterial elicitors such as flg22 or elf18. The induction of alamethicin resistance was independent of novel protein synthesis. Also, the permeabilisation was unaffected by the membrane-depolarising agent FCCP. As judged by lipid analyses, isolated plasma membranes from cellulase-pretreated tobacco cells contained less negatively charged phospholipids (PS and PI), yet higher ratios of membrane lipid fatty acid to sterol and to protein, as compared to control membranes. Conclusion We suggest that altered membrane lipid composition as induced by cellulase activity may render the cells resistant to alamethicin. This induced resistance could reflect a natural process where the plant cells alter their sensitivity to membranepore-forming agents secreted by Trichoderma spp. to attack other microorganisms, and thus adding to the beneficial effect that Trichoderma has for plant root growth. Furthermore, our data extends previous reports on artificial membranes on the importance of lipid packing and charge for alamethicin permeabilisation to in vivo conditions. PMID:21156059

Block polymer-based templates have been utilized in a number of membrane applications; however, there has yet to be a demonstration of a nanoporous block polymer thin film that can achieve high flux and high selectivity simultaneously while also allowing for the facile tuning of the pore wall chemistry. Here, we demonstrate that by synthesizing and controlling the solution self-assembly of a triblock terpolymer, polyisoprene- b-polystyrene- b-poly(N, N-dimethylacrylamide) (PI-PS-PDMA), and precisely inducing non-solvent induced phase separation during the self-assembly process allows for the creation of an asymmetric nanoporous membrane with PDMA-lined pore walls. This PDMA functionality is then converted to any number of side chain functionalities through simple chemistry in the solid state. In this way, we are able to show a highly selectivity membrane that can separate analytes of interest based both on size and chemical composition at a high solution flux. In fact, this high fidelity structure has a very narrow distribution of pore sizes (<10% variation in diameter) over large areas (>500 cm2) . This has allowed for the separation of particles with hydrodynamic radii as low as 0.8 nm, which is the smallest separation achieved using a block polymer-based membrane to date.

The insecticidal nature of Cry {delta}-endotoxins produced by Bacillus thuringiensis is generally believed to be caused by their ability to form lytic pores in the midgut cell membrane of susceptible insect larvae. Here we have analyzed membrane-associated structures of the 65-kDa dipteran-active Cry4Ba toxin by electron crystallography. The membrane-associated toxin complex was crystallized in the presence of DMPC via detergent dialysis. Depending upon the charge of the adsorbed surface, 2D crystals of the oligomeric toxin complex have been captured in two distinct conformations. The projection maps of those crystals have been generated at 17 A resolution. Both complexes appeared to be trimeric; as in one crystal form, its projection structure revealed a symmetrical pinwheel-like shape with virtually no depression in the middle of the complex. The other form revealed a propeller-like conformation displaying an obvious hole in the center region, presumably representing the toxin-induced pore. These crystallographic data thus demonstrate for the first time that the 65-kDa activated Cry4Ba toxin in association with lipid membranes could exist in at least two different trimeric conformations, conceivably implying the closed and open states of the pore.

This study investigated the applicability of membrane distillation (MD) to treat dyeing wastewater discharged by the textile industry. Four different dyes containing methylene blue (MB), crystal violet (CV), acid red 18 (AR18), and acid yellow 36 (AY36) were tested. Two types of hydrophobic membranes made of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) were used. The membranes were characterized by testing against each dye (foulant-foulant) and the membrane-dye (membrane-foulant) interfacial interactions and their mechanisms were identified. The MD membranes possessed negative charges, which facilitated the treatment of acid and azo dyes of the same charge and showed higher fluxes. In addition, PTFE membrane reduced the wettability with higher hydrophobicity of the membrane surface. The PTFE membrane evidenced especially its resistant to dye absorption, as its strong negative charge and chemical structure caused a flake-like (loose) dye-dye structure to form on the membrane surface rather than in the membranepores. This also enabled the recovery of flux and membrane properties by water flushing (WF), thereby direct-contact MD with PTFE membrane treating 100 mg/L of dye mixtures showed stable flux and superior color removal during five days operation. Thus, MD shows a potential for stable long-term operation in conjunction with a simple membrane cleaning process, and its suitability in dyeing wastewater treatment. PMID:27486044

In the paper, we proposed an evolution process of polyvinylidene fluoride (PVDF) macromolecular aggregation in a mixed solvent through the simple and slow gelation process at room temperature. The mixed solvent is prepared with a room-temperature solvent and a high-temperature solvent. The evolution process can be terminated by quenching and exchanging with nonsolvent in a nonsolvent coagulation bath properly, and then the vivid petal-like nanostructure and microspherulite is formed simultaneously. This hierarchical morphology endows PVDF with superhydrophobic and self-cleaning properties, which is useful to PVDF coating and membrane materials. The evolution processes are investigated through the measurements of differential scanning calorimetry (DSC), X-ray diffraction (XRD). In addition, the rheological properties of solution, dry gel and wet gel, are explored. PMID:23725003

Porin, also termed the voltage-dependent anion channel, is the most abundant protein of the mitochondrial outer membrane. The process of import and assembly of the protein is known to be dependent on the surface receptor Tom20, but the requirement for other mitochondrial proteins remains controversial. We have used mitochondria from Neurospora crassa and Saccharomyces cerevisiae to analyze the import pathway of porin. Import of porin into isolated mitochondria in which the outer membrane has been opened is inhibited despite similar levels of Tom20 as in intact mitochondria. A matrix-destined precursor and the porin precursor compete for the same translocation sites in both normal mitochondria and mitochondria whose surface receptors have been removed, suggesting that both precursors utilize the general import pore. Using an assay established to monitor the assembly of in vitro-imported porin into preexisting porin complexes we have shown that besides Tom20, the biogenesis of porin depends on the central receptor Tom22, as well as Tom5 and Tom7 of the general import pore complex (translocase of the outer mitochondrial membrane [TOM] core complex). The characterization of two new mutant alleles of the essential pore protein Tom40 demonstrates that the import of porin also requires a functional Tom40. Moreover, the porin precursor can be cross-linked to Tom20, Tom22, and Tom40 on its import pathway. We conclude that import of porin does not proceed through the action of Tom20 alone, but requires an intact outer membrane and involves at least four more subunits of the TOM machinery, including the general import pore. PMID:11266446

In this study we used live-cell immunocytochemistry and confocal microscopy to study the release from a single vesicle in a simplified system called membrane lawns. The lawns were prepared by exposing differentiated pituitary prolactin (PRL)-secreting cells to a hypoosmotic shear stress. The density of the immunolabeled ternary soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) complexes that bind complexin was approximately 10 times lower than the PRL-positive, lawn-resident vesicles; this indicates that some but not all vesicles are associated with ternary SNARE complexes. However, lawn-resident PRL vesicles colocalized relatively well with particular SNARE proteins: synaptobrevin 2 (35%), syntaxin 1 (22%), and 25-kDa synaptosome associated protein (6%). To study vesicle discharge, we prepared lawn-resident vesicles, derived from atrial natriuretic peptide tagged with emerald fluorescent protein (ANP.emd)-transfected cells, which label vesicles. These maintained the structural passage to the exterior because approximately 40% of ANP.emd-loaded vesicles were labeled by extracellular PRL antibodies. Cargo release from the lawn-resident vesicles, monitored by the decline in the ANP.emd fluorescence intensity, was similar to that in intact cells. It is likely that SNARE proteins are required for calcium-dependent release from these vesicles. This is because the expression of the dominant-negative SNARE peptide, which interferes with SNARE complex formation, reduced the number of PRL-positive spots per cell (PRL antibodies placed extracellularly) significantly, from 58 ± 9 to 4 ± 2. In dominant-negative SNARE-treated cells, the PRL-positive area was reduced from 0.259 ± 0.013 to 0.123 ± 0.014 μm(2), which is consistent with a hindered vesicle luminal access for extracellular PRL antibodies. These results indicate that vesicle discharge is regulated by SNARE-mediated fusion pore widening. PMID:23372020

The effect of surface-potential modulators on palmitate/Ca2+-induced formation of lipid pores was studied in liposomal and inner mitochondrial membranes. Pore formation was monitored by sulforhodamine B release from liposomes and swelling of mitochondria. ζ-potential in liposomes was determined from electrophoretic mobility. Replacement of sucrose as the osmotic agent with KCl decreased negative ζ-potential in liposomes and increased resistance of both mitochondria and liposomes to the pore inducers, palmitic acid, and Ca2+. Micromolar Mg2+ also inhibited palmitate/Ca2+-induced permeabilization of liposomes. The rate of palmitate/Ca2+-induced, cyclosporin A-insensitive swelling of mitochondria increased 22% upon increasing pH from 7.0 to 7.8. At below the critical micelle concentration, the cationic detergent cetyltrimethylammonium bromide (10 μM) and the anionic surfactant sodium dodecylsulfate (10-50 μM) made the ζ-potential less and more negative, respectively, and inhibited and stimulated opening of mitochondrial palmitate/Ca2+-induced lipid pores. Taken together, the findings indicate that surface potential regulates palmitate/Ca2+-induced lipid pore opening. PMID:26014488

The effect of surface-potential modulators on palmitate/Ca2+-induced formation of lipid pores was studied in liposomal and inner mitochondrial membranes. Pore formation was monitored by sulforhodamine B release from liposomes and swelling of mitochondria. ζ-potential in liposomes was determined from electrophoretic mobility. Replacement of sucrose as the osmotic agent with KCl decreased negative ζ-potential in liposomes and increased resistance of both mitochondria and liposomes to the pore inducers, palmitic acid, and Ca2+. Micromolar Mg2+ also inhibited palmitate/Ca2+-induced permeabilization of liposomes. The rate of palmitate/Ca2+-induced, cyclosporin A-insensitive swelling of mitochondria increased 22% upon increasing pH from 7.0 to 7.8. At below the critical micelle concentration, the cationic detergent cetyltrimethylammonium bromide (10 μM) and the anionic surfactant sodium dodecylsulfate (10–50 μM) made the ζ-potential less and more negative, respectively, and inhibited and stimulated opening of mitochondrial palmitate/Ca2+-induced lipid pores. Taken together, the findings indicate that surface potential regulates palmitate/Ca2+-induced lipid pore opening. PMID:26014488

Integrated electrospun nanofibrous membrane was prepared by creating soldered junctions between nanofibers via a facile strategy. Polyacrylonitrile (PAN) mixed with poly(vinylidene fluoride) (PVDF) at different ratios of PVDF were prepared in N,N'-dimethyl formamide (DMF), then electrospun to fabricate PAN/PVDFmembranes. PVDF can form microgels in DMF which slows down volatile speed of DMF and affects the solidification of PAN/PVDF nanofibers. The resulting membranes were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, dynamic water contact angle and tensile testing to confirm the morphology and mechanical properties. Soldered junctions were observed between nanofibers with the increase of PVDF content. These junctions made the membrane integrated and greatly enhanced tensile strength from 5.1 to 8.1 MPa (increased by ~60%) and tensile modulus from 49.4 to 117.9 MPa (increased by ~139%) without compromising porosity when the content of PVDF increased from 0 to 60 wt%. PMID:27398532

Polymeric blends provide a facile route to obtaining materials with various synergistic properties arising from the individual components. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), a hydrophobic polymer, is finding new applications in polymer electrolytes, membranes, and heat-resistant structural materials owing to its high thermal stability, mechanical strength, and weatherability. In this report, blends of PVDF-HFP and polymer brush were prepared with enhanced water uptake and protein resistance, which are important requirements for membranes used in food and biological applications. Polymer brush is composed of poly(methyl methacrylate) main chains, which are miscible with PVDF-HFP, and hydrophilic poly(ethylene glycol) (PEG) brush chains. Incorporation of PEG chains through the polymer brush structure not only enhanced water uptake and protein adsorption resistance but also produced a well-distributed morphology of the blending components through the matrix as evidenced by observation of the morphology after selective extraction of polymer brush from the matrix.

The nuclear pore complex (NPC) is a large protein assembly that mediates molecular trafficking between the cytoplasm and the nucleus. NPCs assemble twice during the cell cycle in metazoans: postmitosis and during interphase. In this study, using small interfering RNA (siRNA) in conjunction with a cell fusion–based NPC assembly assay, we demonstrated that poremembrane protein (Pom)121, a vertebrate-specific integral membrane nucleoporin, is indispensable for an early step in interphase NPC assembly. Functional domain analysis of Pom121 showed that its nuclear localization signals, which bind to importin β via importin α and likely function with RanGTP, play an essential role in targeting Pom121 to the interphase NPC. Furthermore, a region of Pom121 that interacts with the inner nuclear membrane (INM) and lamin B receptor was found to be crucial for its NPC targeting. Based on these findings and on evidence that Pom121 localizes at the INM in the absence of a complete NPC structure, we propose that the nuclear migration of Pom121 and its subsequent interaction with INM proteins are required to initiate interphase NPC assembly. Our data also suggest, for the first time, the importance of the INM as a seeding site for “prepores” during interphase NPC assembly. PMID:21289085

Polymeric membranes prepared via DIPS (Diffusion Induced Phase Separation) are widely studied and utilized as scaffolds for the regeneration of tissue. In this work, poly (L)-lactide membrane are prepared through a DIPS protocol starting from a ternary solution made of polymer, dioxane (solvent) and water (non-solvent). A three-dimensional, porous and mechanically stable membrane is desirable for ingrowth of human bronchial epithelial cells.

With the well established importance of the coupling of water and protons through electroosmotic drag in operating PEFCs the authors present here a derivation of a mathematical model that focuses on the computation of the mobility of an hydronium ion through an arbitrary cylindrical pore of a PEM with a non-uniform charge distribution on the walls of the pore. The total Hamiltonian is derived for the hydronium ion as it moves through the hydrated pore and is effected by the net potential due to interaction with the solvent molecules and the pendant side chains. The corresponding probability density is derived through solution of the Liouville equation. This probability density is then used to compute the friction tensor for the hydronium ion. The authors find two types of contributions: (a) due to the solvent-ion interactions for which they adopt the conventional continuum model; (b) due to the interaction between the pendant charges and the hydronium ion. The latter is a new result and displays the role of the non-uniform nature of the charge distribution on the pore wall.

The pit membrane (PM) is a primary cell wall barrier that separates adjacent xylem water conduits, limiting the spread of xylem-localized pathogens and air embolisms from one conduit to the next. This paper provides a characterization of the size of the pores in the PMs of grapevine (Vitis vinifera). The PM porosity (PMP) of stems infected with the bacterium Xylella fastidiosa was compared with the PMP of healthy stems. Stems were infused with pressurized water and flow rates were determined; gold particles of known size were introduced with the water to assist in determining the size of PM pores. The effect of introducing trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA), oligogalacturonides, and polygalacturonic acid into stems on water flux via the xylem was also measured. The possibility that cell wall-degrading enzymes could alter the pore sizes, thus facilitating the ability of X. fastidiosa to cross the PMs, was tested. Two cell wall-degrading enzymes likely to be produced by X. fastidiosa (polygalactuoronase and endo-1,4- β -glucanase) were infused into stems, and particle passage tests were performed to check for changes in PMP. Scanning electron microscopy of control and enzyme-infused stem segments revealed that the combination of enzymes opened holes in PMs, probably explaining enzyme impacts on PMP and how a small X. fastidiosa population, introduced into grapevines by insect vectors, can multiply and spread throughout the vine and cause Pierce's disease. PMID:20107028

PVDF is a very important piezoelectric polymer material which has a promising range of applications in a variety of fields such as acoustic sensors and transducers, electrical switches, medical instrumentation, artificial sensitive skin in robotics, automotive detection on roads, nondestructive testing, structural health monitoring and as a biocampatible material. In this research cantilever based multi energy harvester was developed to maximize the power output of PVDF sensor. Nano mixture containing ferrofluid (FF) and ZnO nano particles were used to enhance the piezoelectric output of the sensor. The samples were tested under different energy conditions to observe the behavior of nano coated PVDF film under multi energy conditions. Composition of the ZnO and FF nano particles were changed by weight, in order to achieve the optimal composition of the nano mixture. Light energy, vibration energy, combined effect of light and vibration energy, and magnetic effect were used to explore the behavior of the sensor. The sensor with 60% ZnO and 40% FF achieved a maximum power output of 10.7 microwatts when it is under the combined effect of light and vibration energy. Which is nearly 16 times more power output than PVDF sensor. When the magnetic effect is considered the sensor with 100% FF showed the highest power output of 11.2 microwatts which is nearly 17 times more power output than pure PVDF. The effective piezoelctric volume of the sensor was 0.017 cm3. In order to explore the effect of magnetic flux, cone patterns were created on the sensor by means of a external magnetic field. Stability of the cones generated on the sensor played a major role in generated power output.

This paper describes the surface modification of macroporous membranes using ATRP (atom transfer radical polymerization) to create cation-exchange adsorbers with high protein binding capacity at high product throughput. The work is motivated by the need for a more economical and rapid capture step in downstream processing of protein therapeutics. Membranes with three reported nominal pore sizes (0.2, 0.45, 1.0 μm) were modified with poly(3-sulfopropyl methacrylate, potassium salt) tentacles, to create a high density of protein binding sites. A special formulation was used in which the monomer was protected by a crown ether to enable surface-initiated ATRP of this cationic polyelectrolyte. Success with modification was supported by chemical analysis using Fourier-transform infrared spectroscopy and indirectly by measurement of pure water flux as a function of polymerization time. Uniformity of modification within the membranes was visualized with confocal laser scanning microscopy. Static and dynamic binding capacities were measured using lysozyme protein to allow comparisons with reported performance data for commercial cation-exchange materials. Dynamic binding capacities were measured for flow rates ranging from 13 to 109 column volumes (CV)/min. Results show that this unique ATRP formulation can be used to fabricate cation-exchange membrane adsorbers with dynamic binding capacities as high as 70 mg/mL at a throughput of 100 CV/min and unprecedented productivity of 300 mg/mL/min. PMID:23175597

The hERG1 gene (Kv11.1) encodes a voltage-gated potassium channel. Mutations in this gene, lead to one form of the Long QT Syndrome in humans (LQTS). Promiscuous binding of drugs to hERG1 is known to alter the structure/function of the channel leading to an acquired form of the LQTS. Expectably, creation and validation of reliable 3D model of the channel has been a key target in molecular cardiology and pharmacology for the last decade. While many models were built, they all were limited to pore domain. In this work, a full model of the hERG1 channel is developed which includes all trans-membrane segments. We tested a template-driven de-novo design with ROSETTA-membrane modeling using side-chain placements optimized by subsequent molecular dynamics (MD) simulations. While backbone templates for the homology modeled parts of the pore and voltage sensors were based on the available structures of KvAP, Kv1.2 and Kv1.2–Kv2.1 chimera channels, the missing parts are modeled de-novo. The impact of several alignments on the structure of the S4 helix in the voltage-sensing domain was also tested. Herein, final models are evaluated for consistency to the reported structural elements discovered mainly on the basis of mutagenesis and electrophysiology. These structural elements include: salt bridges and close contacts in the voltage-sensor domain; and the topology of the extracellular S5-pore linker compared to that established by toxin foot-printing and NMR studies. Implications of the refined hERG1 model to binding of blockers and channels activators (potent new ligands for channel activations) are discussed. PMID:20740484

A facile fabrication strategy via electrospinning and followed by in situ polymerization to fabricate a patterned, highly stretchable, and conductive polyaniline/poly(vinylidene fluoride) (PANI/PVDF) nanofibrous membrane is reported. Owing to the patterned structure, the nanofibrous PANI/PVDF strain sensor can detect a strain up to 110%, for comparison, which is 2.6 times higher than the common nonwoven PANI/PVDF mat and much larger than the previously reported values (usually less than 15%). Meanwhile, the conductivity of the patterned strain sensor shows a linear response to the applied strain in a wide range from 0% to about 85%. Additionally, the patterned PANI/PVDF strain sensor can completely recover to its original electrical and mechanical values within a strain range of more than 22%, and exhibits good durability over 10 000 folding-unfolding tests. Furthermore, the strain sensor also can be used to detect finger motion. The results demonstrate promising application of the patterned nanofibrous membrane in flexible electronic fields.A facile fabrication strategy via electrospinning and followed by in situ polymerization to fabricate a patterned, highly stretchable, and conductive polyaniline/poly(vinylidene fluoride) (PANI/PVDF) nanofibrous membrane is reported. Owing to the patterned structure, the nanofibrous PANI/PVDF strain sensor can detect a strain up to 110%, for comparison, which is 2.6 times higher than the common nonwoven PANI/PVDF mat and much larger than the previously reported values (usually less than 15%). Meanwhile, the conductivity of the patterned strain sensor shows a linear response to the applied strain in a wide range from 0% to about 85%. Additionally, the patterned PANI/PVDF strain sensor can completely recover to its original electrical and mechanical values within a strain range of more than 22%, and exhibits good durability over 10 000 folding-unfolding tests. Furthermore, the strain sensor also can be used to detect finger

We address the fundamental questions surrounding the nature of water and chemical transport processes deep within sedimentary basin and accretionary-wedge environments. Consolidation and permeability studies conducted to 165 MPa (~10km depth) indicate that ultra-tight clay formations (10-18 m2 to10-21 m2) can substantially modify the fluids migrating through then. Pore-water extractions conducted on smectite/illite rich core samples obtained from 1-3 km depths at IODP (NanTroSEIZE, Chikyu) deep-riser drilling Site C0002, at the elevated loads required to squeeze waters from such deeply buried sediment (stresses up to 100 MPa),resulted in anomalous patterns of sequential freshening with progressive loading. More accurate laboratory investigations (both incremental loading and Constant Rate of Strain test) revealed that such freshening initiates above 20 MPa and progresses with consolidation to become greater than 20% by effective normal load of 165 MPa. Log-log plots of stress vs. hydraulic conductivity reveal that trends remain linear to elevated stresses and total porosities as low at 14%. The implications are that stress induced smectite dehydration and/or membrane filtration effects cause remarkable changes in pore water chemistry with fluid migration through deep, tight, clay-rich formations. These changes should occur in addition to any thermally induced diagenetic and clay-dehydration effects on pore water chemistry. Work is progressing to evaluate the impact of clay composition and temperature to ascertain if purely illitic compositions show similar trends and if the mass fractionation of water and other isotopes also occurs. Such studies will ascertain if the presence of smectite is a prerequisite for freshening or if membrane filtration is a major process in earth systems containing common clay minerals. The results have major implications for interpretations of mass chemical balances, pore water profiles, and the hydrologic, geochemical, and stress state

The addition of the channel-forming domain of colicin E1 to liposomes elicited the transmembrane diffusion (flip-flop) of lipids concomitant to the release of the fluorescent dye from liposomes. Good correlation was found between kinetic and concentration dependences of the two processes. Both the liposome leakage and the lipid flip-flop were stimulated upon alkalinization of the buffer solution after colicin binding at acidic pH. These results in combination with the analysis of the data on colicin binding to liposomes provide evidence in favor of the validity of the toroidal (proteolipidic) pore model as the mechanism of colicin channel formation. PMID:20636264

Clostridium perfringens epsilon toxin (ET) is a potent pore-forming cytotoxin causing fatal enterotoxemia in livestock. ET accumulates in brain and kidney, particularly in the renal distal-collecting ducts. ET binds and oligomerizes in detergent-resistant membranes (DRMs) microdomains and causes cell death. However, the causal linkage between membrane permeabilization and cell death is not clear. Here, we show that ET binds and forms 220-kDa insoluble complexes in plasma membrane DRMs of renal mpkCCD(cl4) collecting duct cells. Phosphatidylinositol-specific phospholipase C did not impair binding or the formation of ET complexes, suggesting that the receptor for ET is not GPI anchored. ET induced a dose-dependent fall in the transepithelial resistance and potential in confluent cells grown on filters, transiently stimulated Na+ absorption, and induced an inward ionic current and a sustained rise in [Ca2+]i. ET also induced rapid depletion of cellular ATP, and stimulated the AMP-activated protein kinase, a metabolic-sensing Ser/Thr kinase. ET also induced mitochondrial membrane permeabilization and mitochondrial-nuclear translocation of apoptosis-inducing factor, a potent caspase-independent cell death effector. Finally, ET induced cell necrosis characterized by a marked reduction in nucleus size without DNA fragmentation. DRM disruption by methyl-beta-cyclodextrin impaired ET oligomerization, and significantly reduced the influx of Na+ and [Ca2+]i, but did not impair ATP depletion and cell death caused by the toxin. These findings indicate that ET causes rapid necrosis of renal collecting duct cells and establish that ATP depletion-mediated cell death is not strictly correlated with the plasma membrane permeabilization and ion diffusion caused by the toxin. PMID:17567938

Seawater pretreatment by gravity-driven membrane (GDM) filtration at 40 mbar has been investigated. In this system, a beneficial biofilm develops on the membrane that helps to stabilize flux. The effects of membrane type, prefiltration and system configuration on stable flux, biofilm layer properties and dissolved carbon removal were studied. The results show that the use of flat sheet PVDFmembranes with pore sizes of 0.22 and 0.45 μm in GDM filtration achieved higher stabilized permeate fluxes (7.3-8.4 L/m(2)h) than that of flat sheet PES 100 kD membranes and hollow fibre PVDF 0.1 μm membranes. Pore constriction and cake filtration were identified as major membrane fouling mechanisms, but their relative contributions varied with filtration time for the various membranes. Compared to raw seawater, prefiltering of seawater with meshes at sizes of 10, 100 and 1000 μm decreased the permeate flux, which was attributed to removal of beneficial eukaryotic populations. Optical coherence tomography (OCT) showed that the porosity of the biofouling layer was more significantly related with permeate flux development rather than its thickness and roughness. To increase the contact time between the biofilm and the dissolved organics, a hybrid biofilm-submerged GDM reactor was evaluated, which displayed significantly higher permeate fluxes than the submerged GDM reactor. Although integrating the biofilm reactor with the membrane system displayed better permeate quality than the GDM filtration cells, it could not effectively reduce dissolved organic substances in the seawater. This may be attributed to the decomposition/degradation of solid organic substances in the feed and carbon fixation by the biofilm. Further studies of the dynamic carbon balance are required. PMID:26900974

Energy harvesting using piezoelectric nanomaterial provides an opportunity for advancement towards self-powered electronics. The fabrication complexities and limited power output of these nano/micro generators have hindered these advancements thus far. This thesis presents a fabrication technique with electrospinning using a grounded cylinder as the collector. This method addresses the difficulties with the production and scalability of the nanogenerators. The non-aligned nanofibers are woven into a textile form onto the cylindrical drum that can be easily removed. The electrical poling and mechanical stretching induced by the electric field and the drum rotation increase the concentration of the piezoelectric beta phase in the PVDF nanofabric. The nanofabric is placed between two layers of polyethylene terephthalate (PET) that have interdigitated electrodes painted on them with silver paint. Applying continuous load onto the flexible PVDF nanofabric at 35Hz produces a peak voltage of 320 mV and maximum power of 2200 pW/(cm2) .

The impendance of np-LiCoO2+xPVDF, as a cathode material candidate for lithium-ion battery (LIB), has been characterized using impedance spectroscopy for x = 0, 5, 10, 15 and 20 volume percentage (%v/v) and for frequencies in the 42 Hz to 5 MHz range. Both real and imaginary components of the impedance were found to be frequency dependent, and both tend to increase for increasing PVDF (polyvinyilidene fluoride) concentration, except that for 10% PVDF both real and imaginary components of impedance are smaller than for 5%. The mechanism for relaxation time for each addition of PVDF was analyzed using Cole-Cole plots. The analysis showed that the relaxation times of the nanostructured LiCoO2 with PVDF additive is relatively constant. Further, PVDF addition increases the bulk resistance and decreases the bulk capacitance of the nanostructured LiCoO2.

The pivotal step on the mitochondrial pathway to apoptosis is permeabilization of the mitochondrial outer membrane (MOM) by oligomers of the B-cell lymphoma-2 (Bcl-2) family members Bak or Bax. However, how they disrupt MOM integrity is unknown. A longstanding model is that activated Bak and Bax insert two α-helices, α5 and α6, as a hairpin across the MOM, but recent insights on the oligomer structures question this model. We have clarified how these helices contribute to MOM perforation by determining that, in the oligomers, Bak α5 (like Bax α5) remains part of the protein core and that a membrane-impermeable cysteine reagent can label cysteines placed at many positions in α5 and α6 of both Bak and Bax. The results are inconsistent with the hairpin insertion model but support an in-plane model in which α5 and α6 collapse onto the membrane and insert shallowly to drive formation of proteolipidic pores. PMID:25228770

The major outer membrane protein Mep45 of Selenomonas ruminantium, an anaerobic Gram-negative bacterium, comprises two distinct domains: the N-terminal S-layer homologous (SLH) domain that protrudes into the periplasm and binds to peptidoglycan, and the remaining C-terminal transmembrane domain, whose function has been unknown. Here, we solubilized and purified Mep45 and characterized its function using proteoliposomes reconstituted with Mep45. We found that Mep45 forms a nonspecific diffusion channel via its C-terminal region. The channel was permeable to solutes smaller than a molecular weight of roughly 600, and the estimated pore radius was 0.58 nm. Truncation of the SLH domain did not affect the channel property. On the basis of the fact that Mep45 is the most abundant outer membrane protein in S. ruminantium, we conclude that Mep45 serves as a main pathway through which small solutes diffuse across the outer membrane of this bacterium. PMID:27310312

Action potentials (APs) are fundamental cellular electrical signals. The genesis of short APs lasting milliseconds is well understood. Ultra-long APs (ulAPs) lasting seconds to minutes also occur in eukaryotic organisms, but their biological functions and mechanisms of generation are largely unknown. Here, we identify TPC3, a previously uncharacterized member of the two-pore channel protein family, as a new voltage-gated Na+ channel (NaV) that generates ulAPs, and that establishes membrane potential bistability. Unlike the rapidly inactivating NaVs that generate short APs in neurons, TPC3 has a high activation threshold, activates slowly and does not inactivate—three properties that help generate long-lasting APs and guard the membrane against unintended perturbation. In amphibian oocytes, TPC3 forms a channel similar to channels induced by depolarization and sperm entry into eggs. TPC3 homologues are present in plants and animals, and they may be important for cellular processes and behaviours associated with prolonged membrane depolarization.

Membranes have been widely used in water remediation (e.g. desalination and heavy metal removal) because of the ability to control membranepore size and surface charge. The incorporation of nanomaterials into the membranes provides added benefits through increased reactivity with different functionality. In this study, we report the dechlorination of 2-chlorobiphenyl in the aqueous phase by a reactive membrane system. Fe/Pd bimetallic nanoparticles (NPs) were synthesized (in-situ) within polyacrylic acid (PAA) functionalized polyvinylidene fluoride (PVDF) membranes for degradation of polychlorinated biphenyls (PCBs). Biphenyl formed in the reduction was further oxidized into hydroxylated biphenyls and benzoic acid by an iron-catalyzed hydroxyl radical (OH•) reaction. The formation of magnetite on Fe surface was observed. This combined pathway (reductive/oxidative) could reduce the toxicity of PCBs effectively while eliminating the formation of chlorinated degradation byproducts. The successful manufacturing of full-scale functionalized membranes demonstrates the possibility of applying reactive membranes in practical water treatment. PMID:24954974

The high hydrophobicity of poly(vinylidene fluoride) (PVDF) membrane remains an obstacle to be applied in some purification processes of water or wastewater. Herein, a highly hydrophilic hybrid mesoporous titania membrane composed of mesoporous anatase titania (meso-TiO2) materials inside the three-dimensional (3D) macropores of PVDFmembrane was successfully prepared by using the dual-templated synthesis method combined with solvent extraction and applied as the photocatalytic membrane reactor for the photodegredation of organic dye in water. The structure and the properties of as-prepared hybrid membranes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption–desorption and contact angle measurements. It was found that the hydrophilicity of PVDFmembrane can be significantly improved by filling mesoporous TiO2 inside the 3D macropores of PVDFmembrane. Moreover, such a PVDF/meso-TiO2 hybrid membrane exhibits promising photocatalytic degradation of dye in water due to the existence of mesoporous anatase TiO2 materials inside PVDFmembrane. This study provides a new strategy to simultaneously introduce hydrophilicity and some desirable properties into PVDF and other hydrophobic membranes. PMID:26754440

The high hydrophobicity of poly(vinylidene fluoride) (PVDF) membrane remains an obstacle to be applied in some purification processes of water or wastewater. Herein, a highly hydrophilic hybrid mesoporous titania membrane composed of mesoporous anatase titania (meso-TiO2) materials inside the three-dimensional (3D) macropores of PVDFmembrane was successfully prepared by using the dual-templated synthesis method combined with solvent extraction and applied as the photocatalytic membrane reactor for the photodegredation of organic dye in water. The structure and the properties of as-prepared hybrid membranes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption-desorption and contact angle measurements. It was found that the hydrophilicity of PVDFmembrane can be significantly improved by filling mesoporous TiO2 inside the 3D macropores of PVDFmembrane. Moreover, such a PVDF/meso-TiO2 hybrid membrane exhibits promising photocatalytic degradation of dye in water due to the existence of mesoporous anatase TiO2 materials inside PVDFmembrane. This study provides a new strategy to simultaneously introduce hydrophilicity and some desirable properties into PVDF and other hydrophobic membranes. PMID:26754440

The high hydrophobicity of poly(vinylidene fluoride) (PVDF) membrane remains an obstacle to be applied in some purification processes of water or wastewater. Herein, a highly hydrophilic hybrid mesoporous titania membrane composed of mesoporous anatase titania (meso-TiO2) materials inside the three-dimensional (3D) macropores of PVDFmembrane was successfully prepared by using the dual-templated synthesis method combined with solvent extraction and applied as the photocatalytic membrane reactor for the photodegredation of organic dye in water. The structure and the properties of as-prepared hybrid membranes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption-desorption and contact angle measurements. It was found that the hydrophilicity of PVDFmembrane can be significantly improved by filling mesoporous TiO2 inside the 3D macropores of PVDFmembrane. Moreover, such a PVDF/meso-TiO2 hybrid membrane exhibits promising photocatalytic degradation of dye in water due to the existence of mesoporous anatase TiO2 materials inside PVDFmembrane. This study provides a new strategy to simultaneously introduce hydrophilicity and some desirable properties into PVDF and other hydrophobic membranes.

The association of Bax with mitochondria is an essential step in the implementation of apoptosis. By using a bacterial two-hybrid assay and crosslinking strategies, we have identified TOM22, a component of the translocase of the outer mitochondrial membrane (TOM), as a mitochondrial receptor of Bax. Peptide mapping showed that the interaction of Bax with TOM22 involved the first alpha helix of Bax and possibly two central alpha helices, which are homologous to the pore forming domains of some toxins. Antibodies directed against TOM22 or an antisense knockdown of the expression of TOM22 specifically inhibited the association of Bax with mitochondria and prevented Bax-dependent apoptosis. In yeast, a haploid strain for TOM22 exhibited a decreased expression of TOM22 and mitochondrial association of ectopically expressed human Bax. Our data provide a new perspective on the mechanism of association of Bax with mitochondria as it involves a classical import pathway. PMID:17096026

Sticholysin II (StnII) is a pore-forming toxin from the sea anemone Stichodactyla heliantus which belongs to the large actinoporin family. The toxin binds to sphingomyelin (SM) containing membranes, and shows high binding specificity for this lipid. In this study, we have examined the role of the hydrogen bonding groups of the SM long-chain base (i.e., the 2NH and the 3OH) for StnII recognition. We prepared methylated SM-analogs which had reduced hydrogen bonding capability from 2NH and 3OH. Both surface plasmon resonance experiments, and isothermal titration calorimetry measurements indicated that StnII failed to bind to bilayers containing methylated SM-analogs, whereas clear binding was seen to SM-containing bilayers. StnII also failed to induce calcein release (i.e., pore formation) from vesicles made to contain methylated SM-analogs, but readily induced calcein release from SM-containing vesicles. Molecular modeling of SM docked to the phosphocholine binding site of StnII indicated that the 2NH and 3OH groups were likely to form a hydrogen bond with Tyr135. In addition, it appeared that Tyr111 and Tyr136 could donate hydrogen bonds to phosphate oxygen, thus stabilizing SM binding to the toxin. We conclude that the interfacial hydrogen bonding properties of SM, in addition to the phosphocholine head group, are crucial for high-affinity SM/StnII-interaction. PMID:23376330

The most common mechanism of antibiotic resistance in multiply resistant Pseudomonas cepacia is decreased porin-mediated outer membrane permeability. In some gram-negative organisms this form of antibiotic resistance can be induced by growth in the presence of weak acids, such as salicylates, which suppress porin synthesis. To determine the effects of salicylates on outer membrane permeability of P. cepacia, a susceptible laboratory strain, 249-2, was grown in 10 mM sodium salicylate. Antibiotic susceptibility and uptake, as well as outer membrane protein patterns, were compared between strain 249-2 grown with and without salicylates. The MICs of chloramphenicol, trimethoprim, ciprofloxacin, and ceftazidime were compared between organisms grown in standard and salicylate-containing medium and are as follows: chloramphenicol, 12.5 versus 100 micrograms/ml; trimethoprim, 0.78 versus 3.125 micrograms/ml; ciprofloxacin, 0.4 versus 1.56 micrograms/ml; ceftazidime, 3.125 versus 3.125 micrograms/ml. The permeability of beta-lactam antibiotics was calculated from the rate of hydrolysis of the chromogenic cephalosporin, PADAC. There was no significant difference between strains grown in the presence and absence of salicylate. By using high-pressure liquid chromatography quantitation of loss from culture medium, the effect of 10 mM salicylate on the cellular permeability of chloramphenicol was measured in strain 249-2 by introduction of a plasmid which encodes production of chloramphenicol acetyltransferase. After 1 h of incubation, 18.5% +/- 1.54% versus 70.1% +/- 3.52%, and after 2 h, 4.20% +/- 1.65% versus 41.90% +/- 2.16% remained in supernatants from organisms grown in the absence and presence of 10 mM salicylate, respectively. Outer membrane protein pattern analysis demonstrated the absence of a protein of apparent molecular weight of 40,000 when strain 249-2 was grown in the presence of 10 mM salicylate. To determine whether this protein functioned as a porin

ABSTRACT The discovery that measles virus (MV) uses the adherens junction protein nectin-4 as its epithelial receptor provides a new vantage point from which to characterize its rapid spread in the airway epithelium. We show here that in well-differentiated primary cultures of airway epithelial cells from human donors (HAE), MV infectious centers form rapidly and become larger than those of other respiratory pathogens: human respiratory syncytial virus, parainfluenza virus 5, and Sendai virus. While visible syncytia do not form after MV infection of HAE, the cytoplasm of an infected cell suddenly flows into an adjacent cell, as visualized through wild-type MV-expressed cytoplasmic green fluorescent protein (GFP). High-resolution video microscopy documents that GFP flows through openings that form on the lateral surfaces between columnar epithelial cells. To assess the relevance of the protein afadin, which connects nectin-4 to the actin cytoskeleton, we knocked down its mRNA. This resulted in more-limited infectious-center formation. We also generated a nectin-4 mutant without the afadin-binding site in its cytoplasmic tail. This mutant was less effective than wild-type human nectin-4 at promoting MV infection in primary cultures of porcine airway epithelia. Thus, in airway epithelial cells, MV spread requires the nectin-4/afadin complex and is based on cytoplasm transfer between columnar cells. Since the viral membrane fusion apparatus may open the passages that allow cytoplasm transfer, we refer to them as intercellular membranepores. Virus-induced intercellular pores may contribute to extremely efficient measles contagion by promoting the rapid spread of the virus through the upper respiratory epithelium. IMPORTANCE Measles virus (MV), while targeted for eradication, still causes about 120,000 deaths per year worldwide. The recent reemergence of measles in insufficiently vaccinated populations in Europe and North America reminds us that measles is extremely

BACKGROUND: We have previously shown that the membrane attack complex (MAC) of complement stimulates cell proliferation and that insertion of homologous MAC into the membranes of endothelial cells results in the release of potent mitogens, including basic fibroblast growth factor (bFGF). The mechanism of secretion of bFGF and other polypeptides devoid of signal peptides, such as interleukin 1 (IL-1) is still an open problem in cell biology. We have hypothesized that the homologous MAC pore itself could constitute a transient route for the diffusion of biologically active macromolecules in and out of the target cells. MATERIALS AND METHODS: Human red blood cell ghosts and artificial lipid vesicles were loaded with labeled growth factors, cytokines and IgG, and exposed to homologous MAC. The release of the 125I-macromolecules was followed as a function of time. The incorporation of labeled polypeptides and fluorescent dextran (MW: 10,000) was measured in MAC-impacted human red blood cells and human umbilical endothelial cells (HUVEC), respectively. RESULTS: Homologous MAC insertion into HUVEC resulted in the massive uptake of 10-kD dextran and induced the release of bFGF, in the absence of any measurable lysis. Red blood cell ghosts preloaded with bFGF, IL-1 beta, and the alpha-chain of interferon-gamma (IFN-gamma) released the polypeptides upon MAC insertion, but they did not release preloaded IgG. MAC-impacted ghosts took up radioactive IFN-gamma from the extracellular medium. Vesicles loaded with IL-I released the polypeptide when exposed to MAC. CONCLUSIONS: The homologous MAC pore in its nonlytic form allows for the export of cytosolic proteins devoid of signal peptides that are not secreted through the classical endoplasmic reticulum/Golgi exocytotic pathways. Our results suggest that the release, and perhaps the uptake, of biologically active macromolecules through the homologous MAC pore is a novel biological function of the complement system in mammals

A facile fabrication strategy via electrospinning and followed by in situ polymerization to fabricate a patterned, highly stretchable, and conductive polyaniline/poly(vinylidene fluoride) (PANI/PVDF) nanofibrous membrane is reported. Owing to the patterned structure, the nanofibrous PANI/PVDF strain sensor can detect a strain up to 110%, for comparison, which is 2.6 times higher than the common nonwoven PANI/PVDF mat and much larger than the previously reported values (usually less than 15%). Meanwhile, the conductivity of the patterned strain sensor shows a linear response to the applied strain in a wide range from 0% to about 85%. Additionally, the patterned PANI/PVDF strain sensor can completely recover to its original electrical and mechanical values within a strain range of more than 22%, and exhibits good durability over 10,000 folding-unfolding tests. Furthermore, the strain sensor also can be used to detect finger motion. The results demonstrate promising application of the patterned nanofibrous membrane in flexible electronic fields. PMID:26781815

CEL-III is a Ca(2+)-dependent and galactose-specific lectin purified from the sea cucumber, Cucumaria echinata, which exhibits hemolytic and hemagglutinating activities. Six molecules of CEL-III are assumed to oligomerize to form an ion-permeable pore in the cell membrane. We have determined the crystal structure of CELIII by using single isomorphous replacement aided by anomalous scattering in lead at 1.7 A resolution. CEL-III consists of three distinct domains as follows: the N-terminal two carbohydrate-binding domains (1 and 2), which adopt beta-trefoil folds such as the B-chain of ricin and are members of the (QXW)(3) motif family; and domain 3, which is a novel fold composed of two alpha-helices and one beta-sandwich. CEL-III is the first Ca(2+)-dependent lectin structure with two beta-trefoil folds. Despite sharing the structure of the B-chain of ricin, CEL-III binds five Ca(2+) ions at five of the six subdomains in both domains 1 and 2. Considering the relatively high similarity among the five subdomains, they are putative binding sites for galactose-related carbohydrates, although it remains to be elucidated whether bound Ca(2+) is directly involved in interaction with carbohydrates. The paucity of hydrophobic interactions in the interfaces between the domains and biochemical data suggest that these domains rearrange upon carbohydrate binding in the erythrocyte membrane. This conformational change may be responsible for oligomerization of CEL-III molecules and hemolysis in the erythrocyte membranes. PMID:15194688

The aim of this study was to synthesis drug-loaded fibrous membrane scaffolds for potential applications as wound dressing. Polyvinylidene fluoride (PVDF) fibrous membranes were loaded with enrofloxacin (Enro) drugs by using an electrospinning process, and their mechanical strength, drug release profile and anti-bacterial properties were evaluated. Enro drug-loaded PVDFmembranes exhibited good elasticity, flexibility and excellent mechanical strength. The electrospinning Enro/PVDFmembranes showed a burst drug release in the initial 12h, followed by sustained release for the next 3 days, which was an essential property for antibiotic drugs applied for wound healing. The drug-loaded PVDF fibrous membranes displayed excellent anti-bacterial activity toward Escherichia coli and Staphylococcus aureus. The results suggest that electrospinning PVDFmembrane scaffolds loaded with drugs can be used as wound dressing. PMID:25936562

The effects induced by 1 MeV/amu ion irradiations were compared to those induced by 4-12 MeV/amu irradiations. Structural analysis with infrared spectroscopy (FTIR) was carried out on PVDF irradiated using C and He beams with different fluences. From these spectra it was observed, as a function of fluence, an overall destruction of the polymer, amorphization of the crystalline regions and the creation of in-chain unsaturations. The track dimensions were determined using a previously developed Monte Carlo simulation code and these results were compared to a semiempirical model.

A control system based on a two-channel narrow-band LMS algorithm is used to isolate periodic vibration at low frequencies on a structure composed of a rigid top plate mounted on a flexible receiving plate. The control performance of distributed PVDF error sensors and accelerometer point sensors is compared. For both sensors, high levels of global reduction, up to 32 dB, have been obtained. It is found that, by driving the PVDF strip output voltage to zero, the controller may force the structure to vibrate so that the integration of the strain under the length of the PVDF strip is zero. This ability of the PVDF sensors to act as spatial filters is especially relevant in active control of sound radiation. It is concluded that the PVDF sensors are flexible, nonfragile, and inexpensive and can be used as strain sensors for active control applications of vibration isolation and sound radiation.

This study investigated the gas separation and transport properties of asymmetric mixed matrix membranes (MMM) fabricated from polyetherimide (PEI); Ultem 1000 incorporated with raw and modified halloysite nanotubes (HNT) as filler. The modified HNTs; S-HNTs were prepared by treating HNTs with N-β-(aminoethyl)-γ-aminopropyltrimethoxy silane (AEAPTMS). FESEM, XRD, FTIR, TGA, DSC and pure gas permeation testing were used to characterise the S-HNTs and the fabricated MMMs. In the first part of the experiments, the effect of dope preparation factors such as: ultrasonic sonication period, filler wetting period and priming period were investigated. In the second part, the influence of silane concentration on the fabricated MMMs was studied. Results showed that, increasing the silane concentration, led to higher tendency in HNT agglomeration which resulted in poor separation properties but permeability enhancement. In the last part, the effect of S-HNTs loading was experienced. Our observations showed that the dispersion of nanoparticles decreased with an increase in the S-HNTs loading. Accordingly, 0.5% loading of silylated-HNT yielded the optimum MMMs in terms of permeability (27% increase) and selectivity (8% increase). PMID:21529819

The colicins are bacteriocins that target Escherichia coli and kill bacterial cells through different mechanisms. Colicin A forms ion channels in the inner membranes of nonimmune bacteria. This activity resides exclusively in its C-terminal fragment (residues 387–592). The soluble free form of this domain is a 10 α-helix bundle. The hydrophobic helical hairpin, H8–H9, is buried inside the structure and shielded by eight amphipathic surface helices. The interaction of the C-terminal colicin A domain and several chimeric variants with lipidic vesicles was examined here by isothermal titration calorimetry. In the mutant constructions, natural sequences of the hydrophobic helices H8 and H9 were either removed or substituted by polyalanine or polyleucine. All the constructions fully associated with DOPG liposomes including the mutant that lacked helices H8 and H9, indicating that amphipathic rather than hydrophobic helices were the major determinants of the exothermic binding reactions. Alanine is not specially favored in the lipid-bound form; the chimeric construct with polyalanine produced lower enthalpy gain. On the other hand, the large negative heat capacities associated with partitioning, a characteristic feature of the hydrophobic effect, were found to be dependent on the sequence hydrophobicity of helices H8 and H9. PMID:24047995

This paper studies the cumulative effect of various parameters, namely anionic polyacrylamide (APAM) concentration, oil concentration, pH, trans-membrane pressure (TMP), and total dissolved solid (TDS), and obtains optimal parameters for the minimum relative flux (J/J(0)) declining in aqueous solutions with response surface methodology (RSM). In order to analyze the mutual interaction and optimal values of parameters affecting ultrafiltration, a central composite rotatable design (CCRD), one method of RSM, was employed. The analysis of variance (ANOVA) of the cubic polynomial model demonstrated that this model was highly significant and reliable. The results show that the effect of APAM and oil on J/J(0) has an inverse trend with pH value increasing. Moreover, the mutual interaction of initial APAM (oil) concentration (C(APAM(oil))) and pH (TMP) were negligible, while the mutual interaction of C(APAM) and C(oil) has an obvious effect, i.e. the effect of initial feed C(APAM) became more important at higher values of initial feed C(oil), and the J/J(0) was only about 4%. The favorable operate conditions in this ultrafiltration process were at low C(APAM), C(oil), pH, and TMP, which agreed with the conclusions of many authors, while considering water production, C(APAM) and C(oil) < 50 mg/L, pH < 4, and TMP < 0.075 MPa could be accepted. PMID:21872396

Proposed herein is a new ambient temperature Li+ conducting PVDF-HFP-co-polymer based hybrid polymer electrolyte with polyvinyl carbozole (PVK) as additive. The addition of the latter provides high ambient temperature electrolytic conductivity (σi) 0.7 × 10-3S/cm with an ionic transference number of 0.6, besides providing the thermoplastic flexibility to the whole matrix. The membrane is found to exhibit a wide electrochemical potential window, >4.5V against Li/Li+. When prepared properly, the membrane is dry and free standing, yet totally suitable for lithium polymer rechargeable batteries. This paper presents the preparation, microstructure and electrochemical characteristics of this new hybrid polymeric membrane. Finally, the dry polymeric electrolyte membrane has been employed in a lithium polymer cell against LT-LiCo0.8Ni0.2O2 as positive electrode and its interfacial behavior and electrochemical cycling results are presented.

Multicellular organisms are constantly exposed to a multitude of pathogenic microbes. Infection is inhibited in vivo by the innate and adaptive immune system. Mycobacterium species have emerged that are resistant to most antibiotics. We identified several naturally occurring cationic antimicrobial peptides that were active at low micromolar concentrations against Mycobacterium smegmatis. Human-derived cathelicidin LL-37 is well characterized and studied against M. smegmatis; we compared LL-37 with Chinese cobra-derived cathelicidin NA-CATH and mouse cathelicidin (mCRAMP). Two synthetic 11-residue peptides (ATRA-1A and ATRA-2) containing variations of a repeated motif within NA-CATH were tested for their activity against M. smegmatis along with a short synthetic peptide derivative from the human beta-defensin hBD3 (hBD3-Pep4). We hypothesized that these smaller synthetic peptides may demonstrate antimicrobial effectiveness with shorter length (and at less cost), making them strong potential candidates for development into broad-spectrum antimicrobial compounds or use in combination with antibiotics. These peptides have antimicrobial activity with EC50 ranging from 0.05 to 1.88 μg/mL against Mycobacterium smegmatis. The ATRA-1A short peptide was found to be the most effective antimicrobial peptide (AMP) (EC50 = 0.05 μg/mL). High bactericidal activity correlated with bacterial membrane depolarization and permeabilization activities. The efficacy of the peptides was further analyzed through Minimal Inhibitory Concentration (MIC) assays. The MICs were determined by the microdilution method. The peptide mCRAMP showed the best MIC activity at 15.6 μg/mL. Neither of the effective short synthetic peptides demonstrated synergy with the antibiotic rifampicin, although both demonstrated synergy with the cyclic peptide antibiotic polymyxin B. The peptides LL-37 and mCRAMP displayed synergism with rifampicin in MIC assays, whereas antibiotic polymyxin B displayed synergism

Diverse cell biological processes that involve shaping and remodeling of cell membranes are regulated by membrane lateral tension. Here we focus on the role of tension in driving membrane fusion. We discuss the physics of membrane tension, forces that can generate the tension in plasma membrane of a cell, and the hypothesis that tension powers expansion of membrane fusion pores in late stages of cell-to-cell and exocytotic fusion. We propose that fusion pore expansion can require unusually large membrane tensions or, alternatively, low line tensions of the pore resulting from accumulation in the pore rim of membrane-bending proteins. Increase of the inter-membrane distance facilitates the reaction. PMID:26282924

Nanocomposites have been obtained by dispersing Multi Walled Carbon Nanotubes (MWCNTs) within polyvinylidene fluoride. Various samples loaded by 0 to 20 % wt. MWCNTs have been obtained by melt mixing using a Haake RheoMixer, with two counter rotating screws. The effect of the nanofiller concentration on the glass, melting, and crystallization temperatures, as determined from Differential Scanning Calorimetry measurements, is reported. Small shifts towards higher temperatures as the loading with MWCNTs was increased have been noticed. A detailed analysis on the effect of MWCNTs on the degree of crystallinity of PVDF is reported. Raman data obtained by using a Renishaw InVia spectrometer have been used to estimate the stress transfer. Additional information was obtained by FTIR and Wide Angle X-Ray Scattering. The nature of the crystalline phases was determined for each sample. Thermogravimetric data showed a small increase of the thermal stability of the polymeric matrix upon the loading with MWCNTs.

Polyvinylidene fluoride (PVDF) film has been widely investigated as a sensor and transducer material due to its high piezo-, pyro- and ferroelectric properties. To activate these properties, PVDF films require a mechanical treatment, stretching or poling. In this paper, we report on a force sensor based on PVDF fabrics with excellent flexibility and breathability, to be used as a specific human-related sensor. PVDF nanofibrous fabrics were prepared by using an electrospinning unit and characterized by means of scanning electron microscopy (SEM), FTIR spectroscopy and x-ray diffraction. Preliminary force sensors have been fabricated and demonstrated excellent sensitivity and response to external mechanical forces. This implies that promising applications can be made for sensing garment pressure, blood pressure, heartbeat rate, respiration rate and accidental impact on the human body.

Piezoelectric polymers have been known to exist for more than 40 years, but in recent years they have been recognized as smart materials for the fabrication of microsensors, microactuators and other micro-electro-mechanical systems (MEMS). In this work, femtosecond laser micromachining of a polyvinylidene fluoride (PVDF) film, coated with NiCu on both sides, has been studied to understand selective patterning mechanisms of NiCu layers and ablation characteristics of PVDF films. A detailed characterization of morphological changes of the laser-irradiated areas has been investigated using scanning electron microscopy. Through morphological analysis, the multiple shot damage thresholds of a 28 µm thick PVDF film and 40 nm thick NiCu layer have been determined. Surface morphology examination indicates that NiCu layers are removed from the PVDF film through a sequence of cracking-peeling off-curling. In addition, the NiCu layer on the rear side was also removed by the partially transmitted laser energy. The PVDF film was removed in forms of bundles of filaments and solid fragments by a combination of pure ablation and explosive removal of material by bursting of bubbles; the role of the explosive removal becomes more dominant with the increase of laser fluence. Optimal process conditions for cutting of the PVDF film and patterning of the NiCu coating without damaging the PVDF polymer have been established and applied to fabricate a vibration microsensor prototype that shows significant potential in using PVDF-based functional microdevices for telecommunications, transportation and biomedical applications.

A study of mechanisms of electrotransfection using Escherichia coli (JM 105) and the plasmid DNA pBR322 as model system is reported. pBR322 DNA carries an ampicillin resistance gene: E. coli transformants are conveniently assayed by counting colonies in a selection medium containing 50 micrograms/ml ampicillin and 25 micrograms/ml streptomycin. Samples not exposed to the electric field showed no transfection. In the absence of added cations, the plasmid DNA remains in solution and the efficiency of the transfection was 2 x 10(6)/micrograms DNA for cells treated with a 8-kV/cm, 1-ms electric pulse (square wave). DNA binding to the cell membrane greatly enhanced the efficiency of the transfection and this binding was increased by milimolar concentrations of CaCl2, MgCl2, or NaCl (CaCl2 greater than MgCl2 greater than NaCl). For example, in the presence of 2.5 mM CaCl2, 55% of the DNA added bound to E. coli and the transfection efficiency was elevated by two orders of magnitude (2 x 10(8)/micrograms DNA). These ions did not cause cell aggregation. With a low ratio of DNA to cells (less than 1 copy/cell), transfection efficiency correlated with the amount of DNA bound to the cell surface irrespective of salts. When the DNA binding ratio approached zero, the transfection efficiency was reduced by two to three orders, indicating that DNA entry by diffusion through the bulk solution was less than 1%. Square pulses of up to 12 kV/cm and 1 ms were used in the electrotransfection experiments. When cell concentration was 1 x 1010 cell/ml and DNA was added before the pulse, a transfection efficiency of up to 5 x 108/ microg DNA was obtained under optimum conditions (a single pulse of 8 kV/cm, 1 ms, in the presence of 5 mM CaCl2). When DNA was added to E. coli after the electric pulse, the efficiency of the transfection was dramatically reduced owing to the resealing of pores. Transfection was reduced to zero when DNA was added 2 h after the electroporation. However

A highly sensitive flexible piezoelectric material is developed by using a composite nanofibers web of polymer and metal. The nanofibers webs are made by electrospinning a mixed solution of poly(vinylidene fluoride) (PVDF) and silver nanowires (AgNWs) in the co-solvent of dimethyl formamide and acetone. SEM images show that the obtained webs are composed of AgNWs doped PVDF fibers with diameters ranging from 200nm to 500nm. Our FTIR and XRD results indicate that doping AgNWs into PVDF fiber can enhance the contents of beta phase of the PVDF. UV-Vis spectrum shows a slightly red shift at 324 nm and 341 nm after the AgNWs doping into PVDF, proving the presence of interaction between AgNWs and the PVDF polymer chain. The piezoelectric constant d33 of the nanofibers webs tested with a homemade system, reveals a good agreement with FTIR and XRD characteristic, and the highest one is up to 29.8 pC/N for the nanofibers webs containing 1.5% AgNWs, which is close to that of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE), 77/23). This study may provide a way to develop high-performance flexible sensors.

Phase diagrams of polyvinylidene fluoride (PVDF) and its copolymers with hexafluoropropylene (HFP) and bromotrifluoroethylene (BTFE) are investigated via first-principles simulations and compared to previously studied P(VDF-chlorotrifluoroethylene) (CTFE) data. We find that a nonpolar to polar phase transition induced by an electric field also occurs in HFP and BTFE copolymers and the results for P(VDF-HFP) show good agreement with existing experiments. For P(VDF-BTFE) we show that its nonpolar phase remains the ground state for a substantially larger range of concentrations than for P(VDF-CTFE) and P(VDF-HFP), and predict that a high BTFE concentration copolymer will achieve a significantly higher energy density at low field than P(VDF-CTFE) 9%. The transition pathways connecting the polar and nonpolar phases are also calculated and the energy barriers for the transitions turn out to be similar for the three copolymers, even at different co-monomer concentrations. The similarity of barriers indicates that a mixture of these and related copolymers can be used to optimize the properties of the dielectric, such as energy density, processability, and cost.

We demonstrate that microporous PVDFmembranes sandwiched between multiple layers of nanomaterials can be used for continuous monitoring of glucose level in vivo. This is achieved by coating needle electrodes with Polyaniline nanofiber, Platinum nanoparticles, glucose oxidase enzyme and porous layers, successfully fabricated with layer-by-layer deposition. Nanoparticles incorporated into conductive Polyaniline nanofibers resulted in high surface to volume ratio and electrocatalytic activity for glucose enzyme. A composite coating membrane of porous PVDF and nano-sphere Nafion limited the glucose transportation and increased the lifetime of in vivo measurements. The glucose biosensor exhibited a sub-microamperometric output current, fast response time of less than 30s and a sensitivity of 0.23 μA/mM. The linear sensing range in terms of glucose concentration was from 0 to 20mM. Implantable experiments using mice models showed excellent response to the variation of blood glucose concentration while maintaining biocompatibility with the surrounding tissues. The sensitivity was shown to remain within 10% close to initial sensitivity within the 7 days of continuous monitoring, and maintain at 70% of the initial sensitivity within 21 days. PMID:26276540

In this study, we fabricated a composite membrane for membrane distillation (MD) by modifying a commercial hydrophobic polyvinylidene fluoride (PVDF) membrane with a nanocomposite coating comprising silica nanoparticles, chitosan hydrogel and fluoro-polymer. The composite membrane exhibits asymmetric wettability, with the modified surface being in-air hydrophilic and underwater oleophobic, and the unmodified surface remaining hydrophobic. By comparing the performance of the composite membrane and the pristine PVDFmembrane in direct contact MD experiments using a saline emulsion with 1000 ppm crude oil (in water), we showed that the fabricated composite membrane was significantly more resistant to oil fouling compared to the pristine hydrophobic PVDFmembrane. Force spectroscopy was conducted for the interaction between an oil droplet and the membrane surface using a force tensiometer. The difference between the composite membrane and the pristine PVDFmembrane in their interaction with an oil droplet served to explain the difference in the fouling propensities between these two membranes observed in MD experiments. The results from this study suggest that underwater oleophobic coating can effectively mitigate oil fouling in MD operations, and that the fabricated composite membrane with asymmetric wettability can enable MD to desalinate hypersaline wastewater with high concentrations of hydrophobic contaminants. PMID:26958985

Ferroelectric polymers (PVDF) with well-defined and precisely known electrical properties are now routinely available from commercial sources. Electrical processing with the Bauer cyclic poling method can produce individual films with well-defined remanent polarization up to 9 /spl mu/C/cm/sup 2/. These polymers provide an unusual opportunity to study the structure and physical properties of materials subjected to shock loading. The behavior of PVDF has been studied over a wide range of pressures using high-pressure shock loading and has yielded well-behaved, reproducible data up to 25 GPa in inert materials. The application of PVDF gauges for recording shock waves induced in polar materials such as Kel-F, PMMA, or in reactive materials is hampered by observations of anomalous responses due to shock-induced polarization or an electrical charge released inside a shock-compressed explosive. A solution using an appropriate electrical shielding has been identified and applied to PVDF for shock measurement studies of Kel-F, and for Hugoniot measurements of high explosives (PH). Furthermore, shock pressure profiles obtained with in situ PVDF gauges in porous HE (Formex) in a detonation regime have been achieved. Typical results of shock pressure profile versus time show a fast superpressure of a few nanoseconds followed by a pressure release down to a plateau level and then by a pressure decay. More accurate measurements are reported with electrically improved PVDF gauges as well as with 0.25 mm/sup 2/ active area PVDF gauges. PMID:18238691

In this study, polydopamine (PDA) coated electrospun poly(vinyldiene fluoride) (PVDF) nanofibrous membranes used as separator for lithium-ion batteries are successfully prepared. Their morphology, chemical and electrochemical characterization are investigated. The morphology and porosity measurements of the membranes show that the PDA coating does not harm to the structure of the electrospun PVDF nanofibrous membranes. Due to the PDA coating, it makes the PVDF surface hydrophilic and thus increases the electrolyte uptake and ionic conductivity, resulting in the enhanced performance of batteries. The battery using the PDA coated PVDF nanofibrous separator exhibits better cycling performance and higher power capability than that the battery using the bare PVDF nanofibrous separator. This study underlines that the PDA-coating treatment provides a promising process for the fabrication of advanced electrospun nanofibers separator in the lithium-ion battery applications.

Standard immunoblotting procedures were unable to detect metallothioneins-1 and 2 (MT-1, MT-2) and metallothionein-3 (MT-3)/growth inhibitory factor (GIF) in unfractionated brain homogenates. We have developed a novel process which involves the inclusion of 2 mM CaCl2 in electrophoretic transfer buffers and glutaraldehyde fixation following transfer to either nitrocellulose or polyvinylidene difluoride (PVDF) membranes. Using commercial MT antibodies and a specific MT-3 polyclonal antibody raised in our laboratory, we have been able to detect all three MTs on both membrane types with a detection limit of approx. 10 ng for MT-1 and MT-2. Nitrocellulose membranepore size had no noticeable effect on detection sensitivity. These modifications enable more sensitive MT detection than previously described blotting methods. In addition, this technique eliminates the need for indirect monitoring approaches and simplifies quantification since sample fractionation or enrichment are not required. PMID:8796480

Membranes with more resilience to abrasive wear are highly desired in water treatment, especially for seawater desalination. Nanocomposite poly(vinylidene fluoride) (PVDF)/nanoclay membranes were prepared by phase inversion and then tested for abrasion resistance. Their material properties were characterized using Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), tensile testing, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Nanoclay Cloisite(®) 15A was utilised as the inorganic nanoparticle incorporated into PVDF. FTIR results showed a shifting of the PVDF crystalline phase from α to β thus indicating that the nanoclay altered the PVDF host material's structure and mechanical properties in terms of stiffness and toughness. Water permeation test showed that nanoclay at low concentration tended to reduce water flux. All nanocomposite membranes, with between 1 wt% and 5 wt% initial nanoclay loading, were more abrasion resistant than the control PVDFmembrane. However, the 1 wt% exhibited superior resistance, lasting two times longer than the reference PVDFmembrane under the same abrasive condition. The 1 wt% nanoclay membrane appeared less abraded by SEM observation, while also having the greatest tensile strength improvement (from 4.5 MPa to 4.9 MPa). This membrane also had the smallest agglomerated nanoclay particle size and highest toughness compared to the higher nanoclay content membranes. Nanoclays are therefore useful for improving abrasion resistance of PVDFmembranes, but optimal loadings are essential to avoid losing essential mechanical properties. PMID:24698723

Time-resolved measurements of pressure profiles from the detonation of explosive devices have proven to be essential for detailed study of device performance. At present such measurements are routinely carried out with laser velocity interferometer (VISAR) systems, electromagnetic particle velocity gauges or piezoresistant (Manganin) gauges. One of the most promising new gauges to appear in recent years is the piezoelectric polymer gauge (PVDF) which has been standardized for general use based on the materials processing techniques developed by Bauer. The special problems presented by small size piezoelectric polymer gauges and nonplanar impacts are studied over a range of impact conditions. The response of 1 mm by 1 mm active area PVDF gauges under precisely controlled compressed-gas gun impacts shows highly reproducible results to pressures of 20 GPa. For the PVDF gauge which is placed within 12 microns of the impact surface and under approximately planar loading with small detonator flyer plates, PVDF gauge signals appear to be reduced by about 15% compared to the compressed-gas gun loading response. For highly nonplanar flyer impacts the PVDF signals are reduced by about 35%. In all stress environments, high quality, time-resolved current pulses are observed. 13 refs., 10 figs., 2 tabs.

A standardized transducer that can respond to shock loading over a large stress range (0.2 to 50.0 GPa) is required for shock wave measurements. A cooperative program has been conducted among our laboratories to provide a well understood and highly reproducible standardized PVDF polymer film gauge to investigate stress wave loading and release. The polymer material source and standardized PVDF piezoelectric stress gauges are based on the work by Bauer. The shock response of standardized PVDF piezoelectric stress gauges produced by SNLA/Ktech, ISL, and commercially has been measured in controlled shock wave experiments using a compressed gas gun. Shock wave response measurements made in the 0.3 to 46.0 Gpa range show excellent agreement among gauges produced by three different facilities. These experiments demonstrated that a repeatable, well understood PVDF stress gauge can be produced if strict specifications are met. These experiments demonstrated PVDF gauges could function repeatably under severe shock loading conditions. Specific applications of this unique stress gauge are also presented. 10 refs., 5 figs., 2 tabs.

A strain sensor based on the composites of poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) filled by multi-walled carbon nanotube (MWNT) was prepared using a proposed fabrication process. Three kinds of MWNT loadings, i.e., 1.0wt.%, 2.0wt.% and 3.0wt.% were employed. Due to good dispersion state of MWNT in PVDF-HFP matrix, which was characterized by scanning electron microscope (SEM), this sensor was found to be of high sensitivity and stable performance. The sensor’s piezoresistivity varied in a weak nonlinear pattern, which was probably caused by the tunneling effect among neighboring MWNTs. The gauge factor of the sensor of 1.0wt.% MWNT loading was identified to be the highest, i.e., 33. This sensor gauge factor decreased gradually with the increase of addition amount of MWNT, which was 5 for the sensor of 3.0wt.% MWNT loading. This gauge factor was still higher than that of conventional metal-foil strain sensors. The electrical conductivity of PVDF-HFP/MWNT composites was also studied. It was found that with the increase of the addition amount of MWNT, the electrical conductivity of the PVDF-HFP/MWNT composites varied in a perfect percolation pattern with a very low percolation threshold, i.e., 0.77 vol.%, further indicating the very good dispersion of MWNT in the PVDF-HFP matrix.

An effective electrode was developed based on electromembrane extraction (EME) and square wave voltammetry (SWV) for simultaneous separation, pre-concentration and determination of lead (II) (Pb(II)) ions in complex aqueous samples. Electrochemically reduced graphene oxide-graphite reinforced carbon (ErGO-GRC) was utilized in conjunction with the SWV. Pb(II) ions were extracted from an aqueous sample solution into an acidic acceptor phase (1M HCl) in the lumen of the polyvinylidene fluoride (PVDF) membrane bag by the application of voltage of maximum 6 V across the supported liquid membrane (SLM), consisting of organic solvent and di-(2-ethylhexyl)phosphoric acid (D2EHPA). The parameters affecting the EME were optimized for Pb(II) ions. The optimum EME conditions were found to be 20% D2EHPA in 1-octanol impregnated in the wall of PVDFmembrane (PVDF17) as the SLM, extraction time of 20 min, pH of sample solution of 8 and a voltage of 5 V. The PVDF-ErGO-GRC electrode system attained enrichment factors of 40 times and 80% of extraction with relative standard deviations (n=5) of 8.3%. Good linearity ranging from 0.25 to 2 nM with coefficients correlation of 0.999 was obtained. The Pb(II) ions detection limit of PVDF-ErGO-GRC electrode was found to be 0.09 nM. The newly developed single setup electrochemical system was applied to complex aqueous samples such as tap, river and sea water to evaluate the feasibility of the method for applications. PMID:26653429

Most membrane attack complex-perforin/cholesterol-dependent cytolysin (MACPF/CDC) proteins are thought to form pores in target membranes by assembling into pre-pore oligomers before undergoing a pre-pore to pore transition. Assembly during pore formation is into both full rings of subunits and incomplete rings (arcs). The balance between arcs and full rings is determined by a mechanism dependent on protein concentration in which arc pores arise due to kinetic trapping of the pre-pore forms by the depletion of free protein subunits during oligomerization. Here we describe the use of a kinetic assay to study pore formation in red blood cells by the MACPF/CDC pneumolysin from Streptococcus pneumoniae. We show that cell lysis displays two kinds of dependence on protein concentration. At lower concentrations, it is dependent on the pre-pore to pore transition of arc oligomers, which we show to be a cooperative process. At higher concentrations, it is dependent on the amount of pneumolysin bound to the membrane and reflects the affinity of the protein for its receptor, cholesterol. A lag occurs before cell lysis begins; this is dependent on oligomerization of pneumolysin. Kinetic dissection of cell lysis by pneumolysin demonstrates the capacity of MACPF/CDCs to generate pore-forming oligomeric structures of variable size with, most likely, different functional roles in biology. PMID:26906727

During the past decade a substantial amount of work has been done in the area of ultrasonic imaging technology using 2D arrays. The main problems arising for the two-dimensional matrix transducers at megahertz frequencies are small size and huge count of the elements, high electrical impedance, low sensitivity, bad SNR and slower data acquisition rate. The major technological difficulty remains the high density of the interconnect. To solve these problems numerous approaches have been suggested. In the present work, a 24×24 elements (24 transmit+24 receive) matrix and a switching board were developed. The transducer consists of two 52 μm PVDF layers each representing a linear array of 24 elements placed one on the top of the other. Electrodes in these two layers are perpendicular and form the grid of 0.5×0.5 mm pitch. The layers are bonded together with the ground electrode being monolithic and located between the layers. The matrix is backed from the rear surface with an epoxy composition. During the emission, a linear element from the emitting layer generates a longitudinal wave pulse propagating inside the test object. Reflected pulses are picked-up by the receiving layer. During one transmit-receive cycle one transmit element and one receive element are selected by corresponding multiplexers. These crossed elements emulate a small element formed by their intersection. The present design presents the following advantages: minimizes number of active channels and density of the interconnect; reduces the electrical impedance of the element improving electrical matching; enables the transmit-receive mode; due to the efficient backing provides bandwidth and good time resolution; and, significantly reduces the electronics complexity. The matrix can not be used for the beam steering and focusing. Owing to this impossibility of focusing, the penetration depth is limited as well by the diffraction phenomena.

In this work, a prototype Polyvinylidene Fluoride (PVDF) tactile sensor for endoscopic application has been developed. The sensor aims to measure hardness, which is one of the information of tactile perceptions, of biomedical tissue. This sensor is composed of two PVDF films, a silicone cylindrical column, and an aluminum cylinder. And the classification of hardness is concerned with the ratio of these PVDF outputs. In this paper, two sensors are fabricated using two silicone cylindrical columns with different Young's modulus. The performance evaluation of each sensor is conducted using 6 silicone rubbers as measuring object. The experimental results correspond with the simplified theoretical analysis and the proposed sensor can distinguish a difference of elastic property.

In this paper the concept of a PVDF based gesture controller is introduced and accompanied by a supporting model derived using Hamilton's principle. The model incorporates strain contributions from two loading situations: beam subject to transverse loading and axial loading. The prototype gesture controller is comprised of a compression sleeve with a spatially shaded PVDF element situated above the extensor muscles of the right forearm. The goal of the gesture controller, at this stage, is to be able to measure and discern forearm muscle activity for three distinct hand gestures. In this study the system was modeled and simulated. Test data was then collected for each hand gesture and compared to simulations.

Sticholysin II (St II) is the most potent cytolysin produced by the sea anemone Stichodactyla helianthus, exerting hemolytic activity via pore formation in membranes. The toxin's N-terminus contains an amphipathic α-helix that is very likely involved in pore formation. We have previously demonstrated that the synthetic peptide StII(1-30) encompassing the 1-30 segment of St II forms pores of similar radius to that of the protein (around 1 nm), being a good model of toxin functionality. Here we have studied the functional and conformational properties of fluorescent analogs of StII(1-30) in lipid membranes. The analogs were obtained by replacing Leu residues at positions 2, 12, 17, and 24 with the intrinsically fluorescent amino acid Trp (StII(1-30L2W), StII(1-30L12W), StII(1-30L17W), or StII(1-30L24W), respectively). The exchange by Trp did not significantly modify the activity and conformation of the parent peptide. The blue-shift and intensity enhancement of fluorescence in the presence of membrane indicated that Trp at position 2 is more deeply buried in the hydrophobic region of the bilayer. These experiments, as well as assays with water-soluble or spin-labeled lipid-soluble fluorescence quenchers suggest an orientation of StII(1-30) with its N-terminus oriented towards the hydrophobic core of the bilayer while the rest of the peptide is more exposed to the aqueous environment, as hypothesized for sticholysins. PMID:23868208

Actinoporins are effective pore-forming toxins produced by sea anemones. These extremely potent, basic 20 kDa proteins readily form pores in membranes that contain sphingomyelin. Much has been learned about the molecular basis of their pore-forming mechanism in recent years. Pore formation is a multi-step process that involves recognition of membrane sphingomyelin, firm binding to the membrane accompanied by the transfer of the N-terminal region to the lipid-water interface and finally pore formation after oligomerisation of three to four monomers. The final conductive pathway is formed by amphipathic alpha-helices, hence actinoporins are an important example of so-called alpha-helical pore-forming toxins. Actinoporins have become useful model proteins to study protein-membrane interactions, specific recognition of lipids in the membrane, and protein oligomerisation in the lipid milieu. Recent sequence and structural data of proteins similar to actinoporins indicate that they are not a unique family restricted to sea anemones as was long believed. An AF domain superfamily (abbreviated from actinoporin-like proteins and fungal fruit-body lectins) was defined and shown to contain members from three animal and two plant phyla. On the basis of functional properties of some members we hypothesise that AF domain proteins are peripheral membrane proteins. Finally, ability of actinoporins to form transmembrane pores has been exploited in some novel biomedical applications. PMID:19268680

Melittin, a bee venom, is a basic amphiphilic peptide, which mainly acts on the lipid matrix of membranes, lysing various cells. To elucidate the molecular mechanism, we investigated its interactions with phospholipid vesicles. The peptide formed a pore with a short lifetime in the membrane, as revealed by the release of an anionic fluorescent dye, calcein, from the liposomes. Our new double-labeling method clarified that the pore size increased with the peptide-to-lipid ratio. Upon the disintegration of the pore, a fraction of the peptides translocated across the bilayer. The pore formation was coupled with the translocation, which was proved by three fluorescence experiments recently developed by our laboratory. A novel model for the melittin pore formation was discussed in comparison with other pore-forming peptides. PMID:9251799

Polyvinylidene fluoride (PVDF) is a polymer with unique characteristics i.e. piezoelectric and ferrroelectric properties. Piezoelectric propertiesof PVDF are determined by the fraction of β-phase structure. Several optimization methods have been developed to improve the piezoelectric properties of PVDF. One of our research efforts is to improve the piezoelectricity of PVDF by electric poling with high electric field 2G V/m. The application of high electric field performed on PVDF films with a thickness of 1 1m. Each sample was made with a deep coating method, with annealing temperature 70°C-110°C. Based on the XRD characterization, we have obtained value of β-fraction of samples after poling are: 56%, 61%, 77%, 81% and 83%, respectively. Therefore, high electric field poling has been able to improve the piezoelectric properties of PVDF films. The PVDF with good piezoelectric properties are potential can did a tes for piezoelectric sensors and actuators devices.

We report Ag nanoparticle induced Electromagnetic Interference (EMI) shielding in a flexible composite films of Ag nanoparticles incorporated graphite/poly-vinylidene difluoride (PVDF). PVDF nanocomposite thin-films were synthesized by intercalating Ag in Graphite (GIC) followed by dispersing GIC in PVDF. The X-ray diffraction analysis and the high-resolution transmission electron microscope clearly dictate the microstructure of silver nanoparticles in graphite intercalated composite of PVDF matrix. The conductivity values of nanocomposites are increased upto 2.5 times when compared to neat PVDF having a value of 2.70 S/cm at 1 MHz. The presence of Ag broadly enhanced the dielectric constant and lowers the dielectric loss of PVDF matrix proportional to Ag content. The EMI shielding effectiveness of the composites is 29.1 dB at 12.4 GHz for the sample having 5 wt. % Ag and 10 wt. % graphite in PVDF.

Broadband impedance measurements of a PVDF shock-pressure gauge are used to build an equivalent circuit for the gauge. The essential components are a gauge capacitance and a low-loss transmission line. Component features are consistent with the physical characteristics. With knowledge of this circuit, troublesome oscillations can be anticipated and prevented.

In this study, the separation properties of Polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were improved by optimizing membrane morphology and structure. The results showed that the PVDFmembrane had better mechanical and separation properties than Fresenius Polysulfone High-Flux (F60S) membrane. The PVDFmembrane tensile stress at break, tensile elongation and bursting pressure were 11.3 MPa, 395% and 0.625 MPa, respectively. Ultrafiltration (UF) flux of pure water reached 108.2 L∙h−1∙m−2 and rejection of Albumin from bovine serum was 82.3%. The PVDF dialyzers were prepared by centrifugal casting. The influences of membrane area and simulate fluid flow rate on dialysis performance were investigated. The results showed that the clearance rate of urea and Lysozyme (LZM) were improved with increasing membrane area and fluid flow rate while the rejection of albumin from bovine serum (BSA) had little influence. The high-flux PVDF dialyzer UF coefficient reached 62.6 mL/h/mmHg. The PVDF dialyzer with membrane area 0.69 m2 has the highest clearance rate to LZM and urea. The clearance rate of LZM was 66.8% and urea was 87.7%. PMID:25807890

In this study, the separation properties of Polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were improved by optimizing membrane morphology and structure. The results showed that the PVDFmembrane had better mechanical and separation properties than Fresenius Polysulfone High-Flux (F60S) membrane. The PVDFmembrane tensile stress at break, tensile elongation and bursting pressure were 11.3 MPa, 395% and 0.625 MPa, respectively. Ultrafiltration (UF) flux of pure water reached 108.2 L∙h-1∙m-2 and rejection of Albumin from bovine serum was 82.3%. The PVDF dialyzers were prepared by centrifugal casting. The influences of membrane area and simulate fluid flow rate on dialysis performance were investigated. The results showed that the clearance rate of urea and Lysozyme (LZM) were improved with increasing membrane area and fluid flow rate while the rejection of albumin from bovine serum (BSA) had little influence. The high-flux PVDF dialyzer UF coefficient reached 62.6 mL/h/mmHg. The PVDF dialyzer with membrane area 0.69 m2 has the highest clearance rate to LZM and urea. The clearance rate of LZM was 66.8% and urea was 87.7%. PMID:25807890

Binary graft copolymerization of pH-sensitive monomers (N,N-dimethylaminoethyl methacrylate, (DMAEMA) and acrylic acid (AAc) onto polyvinylidene fluoride (PVDF) membranes with pore sizes of 0.22 and 0.45 μm was conducted by one and two-steps grafting using a 60Co gamma radiation source (Gammabeam 651 PT). The DMAEMA and AAc monomers were grafted by an oxidative pre-irradiation method in one-step grafting to obtain PDVF-g-(DMAEMA-co-AAc), and both direct irradiation and an oxidative pre-irradiation method were used to obtain the graft copolymer (PVDF-g-DMAEMA)-g-AAc in two-steps grafting. The optimal conditions, such as reaction time, temperature, solvent, monomer concentration and dose, were studied, the aim of this work was to investigate how these factors affecting the graft percent of DMAEMA and AAc prepared in one and two-steps grafting and their structural differences and also characterize the grafting membrane through analytical techniques.

An excellent protein-fouling-resistance performance of the sulfobetaine-grafted PVDF hollow fiber membrane was obtained and the potential of sulfobetaine-grafted PVDFmembrane to resist the oil fouling was confirmed in the filtration solution which contained inorganic electrolyte, sodium chloride (NaCl). The electrolyte-responsive behavior of the sulfobetaine-modified PVDFmembrane was demonstrated by the filtration of NaCl aqueous solution. The grafting amount of the modified PVDF hollow fiber membrane showed a stable value as 680 μg/cm2. An almost complete coverage of the membrane surface by the grafted sulfobetaine polymer contributed to the high hydrophilicity and membrane strength. The membrane surface became denser and the permeate flux reduced with the increase of NaCl concentration. The cyclic filtration experiment showed that during the filtration of the protein solution with 0.05 mol/L of NaCl, the sulfobetaine-grafted PVDFmembrane exhibited an excellent protein-fouling-resistance performance with a high relative flux recovery of 98.2% and a low irreversible fouling extent which was lower 10 times than that of the nascent PVDF hollow fiber membrane. In addition, the sulfobetaine-grafted PVDF hollow fiber membrane showed an oil-fouling-resistance property during the filtration experiment of the oil-in-water emulsion with 0.05 mol/L of NaCl, resulting in an relative flux recovery of about twice that of the nascent PVDFmembrane. The results extended the application of poly(sulfobetaine)-g-PVDF hollow fiber membrane in the fields of bio-separation, artificial oil and wastewater treatment.

In this work, a supported ionic liquid membrane (SILM) was prepared by impregnating a PVDFmembrane with 1-butyl-3-methylimidazolium dicyanamide ([BMIM][DCA]) ionic liquid. This membrane was tested for its permeability to pure gases (CO2, N2 and O2) and ideal selectivities were calculated. The SILM performance was also compared to that of Ion-Jelly® membranes, a new type of gelled membranes developed recently. It was found that the PVDFmembrane presents permeabilities for pure gases similar or lower to those presented by the Ion-Jelly® membranes, but with increased ideal selectivities. This membrane presents also the highest ideal selectivity (73) for the separation of CO2 from N2 when compared with SILMs using the same PVDF support but with different ionic liquids. PMID:25594165

Our objective was to determine the effect of concentration factor (CF) on the removal of serum protein (SP) from skim milk during microfiltration (MF) at 50 °C using a 0.3-μm-pore-size spiral-wound (SW) polymeric polyvinylidene fluoride (PVDF) membrane. Pasteurized (72°C for 16 s) skim milk was MF (50 °C) at 3 CF (1.50, 2.25, and 3.00×), each on a separate day of processing starting with skim milk. Two phases of MF were used at each CF, with an initial startup-stabilization phase (40 min in full recycle mode) to achieve the desired CF, followed by a steady-state phase (90-min feed-and-bleed with recycle) where data was collected. The experiment was replicated 3 times, and SP removal from skim milk was quantified at each CF. System pressures, flow rates, CF, and fluxes were monitored during the 90-min run. Permeate flux increased (12.8, 15.3, and 19.0 kg/m(2) per hour) with decreasing CF from 3.00 to 1.50×, whereas fouled water flux did not differ among CF, indicating that the effect of membrane fouling on hydraulic resistance of the membrane was similar at all CF. However, the CF used when microfiltering skim milk (50°C) with a 0.3-μm polymeric SW PVDFmembrane did affect the percentage of SP removed. As CF increased from 1.50 to 3.00×, the percentage of SP removed from skim milk increased from 10.56 to 35.57%, in a single stage bleed-and-feed MF system. Percentage SP removal from skim milk was lower than the theoretical value. Rejection of SP during MF of skim milk with SW PVDFmembranes was caused by fouling of the membrane, not by the membrane itself and differences in the foulant characteristic among CF influenced SP rejection more than it influenced hydraulic resistance. We hypothesize that differences in the conditions near the surface of the membrane and within the pores during the first few minutes of processing, when casein micelles pass through the membrane, influenced the rejection of SP because more pore size narrowing and plugging occurred at

A novel manganese dioxide (MnO2) nanosheet network grown on nickel/polyvinylidene fluoride (Ni/PVDF) coaxial fiber membrane is successfully fabricated by a three-step route: the polyvinylidene fluoride fiber membrane is prepared by electrospinning method, and then the Ni(shell)/PVDF(core) coaxial fiber membrane with core-shell structure can be obtained by the electroless deposition, and ﬁnally the manganese dioxide nanosheet network grown on Ni/PVDF coaxial fiber membrane can be achieved by using a simple hydrothermal treatment. This as-prepared binder-free and ﬂexible composite membrane is directly used as anode for lithium ion batteries. The excellent electrochemical performance of the composite membrane can be attributed to the unique combinative effects of nanosized MnO2 network and conductive Ni/PVDF fiber matrix as well as the porous structure of composite fiber membrane.

The location and environment of tryptophans in the soluble and membrane-bound forms of Staphylococcus aureus alpha-toxin were monitored using intrinsic tryptophan fluorescence. Fluorescence quenching of the toxin monomer in solution indicated varying degrees of tryptophan burial within the protein interior. N-Bromosuccinimide readily abolished 80% of the fluorescence in solution. The residual fluorescence of the modified toxin showed a blue-shifted emission maximum, a longer fluorescence lifetime as compared to the unmodified and membrane-bound alpha-toxin, and a 5- to 6-nm red edge excitation shift, all indicating a restricted tryptophan environment and deeply buried tryptophans. In the membrane-bound form, the fluorescence of alpha-toxin was quenched by iodide, indicating a conformational change leading to exposure of some tryptophans. A shorter average lifetime of tryptophans in the membrane-bound alpha-toxin as compared to the native toxin supported the conclusions based on iodide quenching of the membrane-bound toxin. Fluorescence quenching of membrane-bound alpha-toxin using brominated and spin-labeled fatty acids showed no quenching of fluorescence using brominated lipids. However, significant quenching was observed using 5- and 12-doxyl stearic acids. An average depth calculation using the parallax method indicated that the doxyl-quenchable tryptophans are located at an average depth of 10 A from the center of the bilayer close to the membrane interface. This was found to be in striking agreement with the recently described structure of the membrane-bound form of alpha-toxin. PMID:10049328

Due to the chemical stability and flexibility, polyvinylidene fluoride (PVDF) membranes are widely used as the topcoat of architectural membrane structures, roof materials of vehicle, tent fabrics, and so on. Further modified PVDFmembrane with superhydrophobic property may be even superior as the coating layer surface. The lotus flower is always considered to be a sacred plant, which can protect itself against water, dirt, and dust. The superhydrophobic surface of lotus leaf is rough, showing the micro- and nanometer scale morphology. In this work, the microreliefs of lotus leaf were mimicked using PVDFmembrane and the nanometer scale peaks on the top of the microreliefs were obtained by the method of chemical vapor deposition from solution. The surface morphology of PVDFmembrane was investigated by scanning electronic microscopy (SEM) and atomic force microscope (AFM). Elemental composition analysis by X-ray photoelectron spectroscopy (XPS) revealed that the material of the nanostructure of PVDFmembrane was polymethylsiloxane. On the lotus-leaf-like PVDFmembrane, the water contact angle and sliding angle were 155° and 4°, respectively, exhibiting superhydrophobic property.

A nanoporous polyvinylidene Fluoride (PVDF) thin film was developed for applications in energy harvesting, medical surgeries, and industrial robotics. This sponge-like nanoporous PVDF structure dramatically enhanced the piezoelectric effect because it yielded considerably large deformation under a small force. A casting-etching method was adopted to make films, which is effective to control the porosity, flexibility, and thickness of the film. The films with various Zinc Oxide (ZnO) mass fractions ranging from 10 to 50% were fabricated to investigate the porosity effect. The piezoelectric coefficient d33 as well as dielectric constant and loss of the films were characterized. The results were analyzed and the optimal design of the film with the right amount of ZnO nanoparticles was determined.

Currently, wearable electronics are increasingly widely used, leading to an increasing need of portable power supply. As a clean and renewable power source, piezoelectric energy harvester can transfer mechanical energy into electric energy directly, and the energy harvester based on polyvinylidene difluoride (PVDF) operating in 31-mode is appropriate to harvest energy from human motion. This paper established a series of theoretical models to predict the performance of 31-mode PVDF energy harvester. Among them, the energy storage one can predict the collected energy accurately during the operation of the harvester. Based on theoretical study and experiments investigation, two approaches to improve the energy harvesting performance have been found. Furthermore, experiment results demonstrate the high accuracies of the models, which are better than 95%. PMID:25114981

There is a clinical need in fixed prosthodontics for aesthetic materials that are biologically compatible. Polymethylmethacrylate (PMMA) has been used extensively in dental applications. Blends of PMMA and polyvinylidene fluoride (PVDF) are a new class of materials that might perform as aesthetic restorative materials. The fracture properties of PMMA have been intensively studied because it is an amorphous glass below 110{degrees}C, thus exhibiting brittle fracture under normal testing conditions below about 85{degrees}C. However, this brittle behavior leads to poor wear resistance. The properties of the matrix can be tailored by blending with PVDF. The blends are composed of homogeneous mixtures of the two polymers at the molecular level. Polyvinylidene fluoride molecules do not contribute to the mechanical yield behavior of the blend but do act as plasticizers. Improvements in the mechanical properties may be achieved by incorporating a filler into the polymer matrix.

Currently, wearable electronics are increasingly widely used, leading to an increasing need of portable power supply. As a clean and renewable power source, piezoelectric energy harvester can transfer mechanical energy into electric energy directly, and the energy harvester based on polyvinylidene difluoride (PVDF) operating in 31-mode is appropriate to harvest energy from human motion. This paper established a series of theoretical models to predict the performance of 31-mode PVDF energy harvester. Among them, the energy storage one can predict the collected energy accurately during the operation of the harvester. Based on theoretical study and experiments investigation, two approaches to improve the energy harvesting performance have been found. Furthermore, experiment results demonstrate the high accuracies of the models, which are better than 95%. PMID:25114981

Homogeneous-reinforced (HR) polyvinylidene fluoride (PVDF) hollow fiber membranes include PVDF polymer solutions (coating layer) and the matrix membrane prepared through the dry-wet spinning process. The performance of HR membranes varies with the polymer concentration in the polymer solutions and is characterized in terms of pure water flux, rejection of protein, porosity, infiltration property, a mechanical strength test, and morphology observations by a field emission scanning electron microscope (FESEM). The results of this study indicate that the tensile strength of the HR PVDFmembranes decreases slights compared with that of the matrix membrane, but the elongation at break increases much more and the hollow fiber membranes are endowed with better flexibility performance. The HR PVDF hollow fiber membranes have a favorable interfacial bonding between the coating layer and the matrix membrane, as shown by FESEM. The infiltration property is characterized by the contact angle experiments. Pure water flux decreases while the rejection ratio with an increase in polymer concentration increasing. The protein solution flux of the HR PVDFmembranes is higher than that of the matrix membrane after 100 min of infiltration.

We computed structural and elastic properties of totally nine phases of poly(vinyldene fluoride) (PVDF) crystals using the density-functional theory (DFT) method with and without inclusion of the dispersion corrections. In addition to the four known crystalline forms, mechanic properties of five theoretically predicted crystalline forms of PVDF are also investigated. The all-trans form Ip exhibits the largest cohesive energy, bulk, and Young's modulus among the nine crystalline forms. The DFT calculations suggest that the δ crystalline forms (IIIau, IIIpu, IIIpd, and IIIad) possess poor chain rigidity among the nine PVDF crystalline forms. In contrast, a change of relative orientation of PVDF chains does not lead to significant change in cohesive energy and mechanic properties. A comparison of the cohesive energies of nine crystalline forms of PVDF suggests that the theoretically proposed crystalline forms of PVDF are quite stable.

Barium titanate (BaTiO3)-polyvinylidene fluoride (PVDF) composite thick films were grown by using aerosol deposition at room temperature with BaTiO3 and PVDF powders. To produce a uniform composition in ceramic and polymer composite films, which show a substantial difference in specific gravity, we used PVDF-coated BaTiO3 powders as the starting materials. An examination of the microstructure confirmed that the BaTiO3 were well distributed in the PVDF matrix in the form of a 0 - 3 compound. The crystallite size in the BaTiO3-PVDF composite thick films was 5 ˜ 50 times higher than that in pure BaTiO3 thick films. PVDF plays a role in suppressing the fragmentation of BaTiO3 powder during the aerosol deposition process and in controlling the relative permittivity.

An MRI compatible PVDF receiver was designed and manufactured for integration into a transcranial therapy array. 4.8 mm diameter, 110 μm thick PVDF film was air-backed by clamping it across brass tubing. A preamplifier was enclosed within the tubing to improve SNR and drive the long coaxial cables required to reach outside the MRI. The receiver was mounted inside a ring element from an existing array. The receiver performance was compared with a commercial needle hydrophone and tested for MRI compatibility. The PVDF receiver displayed a higher sensitivity than the needle hydrophone and a better capability to reject electrical coupling with the transmit element. MRI image artifacts created by the device were small, and diagnostic ultrasound was possible with the device while simultaneously obtaining an MRI image. Microbubble contrast agent was sonicated both directly, and through a fragment of human skull. The transmit/receive pair was successful in sonicating the microbubbles transcranially and detecting the returning microbubble emissions. A second generation receiver with a diameter of 2.4 mm was manufactured, without sacrificing sensitivity, to increase the field of view of the device. Future work will focus on developing a multi-element receiver array and its testing for brain treatment monitoring.

Two-pore channels are members of the voltage-gated ion channel superfamily. They localise to the endolysosomal system and are likely targets for the Ca2+ mobilising messenger NAADP. In this brief review, we relate mutagenesis of the TPC pore to a recently published homology model and discuss how pore mutants are informing us of TPC function. Molecular physiology of these ubiquitous proteins is thus emerging. PMID:27226934

The formation and annihilation of pores in a lipid vesicle membrane is critical to a number of biotechnologies, such as drug delivery. Previous models of vesicle behavior have ignored the influence of topological changes in the vesicle membrane. Here the entire Helfrich model of a vesicle membrane is considered. Topological changes in the vesicle membrane, such as the formation of a pore, are captured through the use of an embedded phase-field model. The numerical method and sample results will be presented.

Cell death by apoptosis is indispensable for proper development and tissue homeostasis in all multicellular organisms, and its deregulation plays a key role in cancer and many other diseases. A crucial event in apoptosis is the formation of protein-permeable pores in the outer mitochondrial membrane that release cytochrome c and other apoptosis-promoting factors into the cytosol. Research efforts over the past two decades have established that apoptotic pores require BCL-2 family proteins, with the proapoptotic BAX-type proteins being direct effectors of pore formation. Accumulating evidence indicates that other cellular components also cooperate with BCL-2 family members to regulate the apoptotic pore. Despite this knowledge, the molecular pathway leading to apoptotic pore formation at the outer mitochondrial membrane and the precise nature of this outer membranepore remain enigmatic. In this issue of PLOS Biology, Kushnareva and colleagues describe a novel kinetic analysis of the dynamics of BAX-dependent apoptotic pore formation recapitulated in native mitochondrial outer membranes. Their study reveals the existence of a hitherto unknown outer mitochondrial membrane factor that is critical for BAX-mediated apoptotic pore formation, and challenges the currently popular view that the apoptotic pore is a purely proteinaceous multimeric assembly of BAX proteins. It also supports the notion that membrane remodeling events are implicated in the formation of a lipid-containing apoptotic pore. PMID:23049484

The atomic structure of subnanometer pores in graphene, of interest due to graphene's potential as a desalination and gas filtration membrane, is demonstrated by atomic resolution aberration corrected transmission electron microscopy. High temperatures of 500 °C and over are used to prevent self-healing of the pores, permitting the successful imaging of open pore geometries consisting of between -4 to -13 atoms, all exhibiting subnanometer diameters. Picometer resolution bond length measurements are used to confirm reconstruction of five-membered ring projections that often decorate the pore perimeter, knowledge which is used to explore the viability of completely self-passivated subnanometer pore structures; bonding configurations where the pore would not require external passivation by, for example, hydrogen to be chemically inert. PMID:26524121

The research work presented here shows the progress realized in the studies of the ferroelectric and piezoelectric properties of Polyvinylidene Flouride (PVDF). An attempt has been made to understand the fundamental phenomena of the mechanism responsible for the functioning of the shock loaded ferroelectric PVDF. Fundamental questions have not yet found a sufficient response. The main parameter which must be taken into account in the standardization process, is the polarization which is fixed at a value of 9.15 +- 0.15 ..mu..C/cm/sup 2/. There are different PVDF, but it seems clear that there is only one piezoelectric PVDF which can be used for shock gauge transducers.

A formal consensus standard for a version of the generic Bauer PVDF shock stress sensor is being defined by a panel broadly experienced in the techniques of PVDF sensor application. The evolving standard addresses points essential to accurate shock measurement with PVDF gauges. It covers the materials, dimensions, proportions, processing, inspection, calibration, certification, tolerances, and application for PVDF elements. The formal standard will be available for voluntary use by the shock stress community as a guide for selection procurement, application, and analysis of this useful new shock measurement tool. 4 refs.

Membrane separation is an effective method for the removal of hazardous materials from wastewater. Halloysite nanotubes (HNTs) were functionalized with 3-aminopropyltriethoxysilane (APTES), and novel polyvinylidene fluoride (PVDF) nanofiltration membranes were prepared by blending with various concentrations of APTES grafted HNTs (A-HNTs). The morphology structure of the membranes were characterized by scanning electron microscope (SEM) and atomic force microscopy (AFM). The contact angle (CA), pure water flux (PWF) and antifouling capacity of membranes were investigated in detail. In addition, the separation performance of membranes were reflected by the removal of dye and heavy metal ions in simulated wastewater. The results revealed that the hydrophilicity of A-HNTs blended PVDFmembrane (A-HNTs@PVDF) was enhanced significantly. Owing to the electrostatic interaction between membrane surface and dye molecules, the dye rejection ratio of 3% A-HNTs@PVDFmembrane reached 94.9%. The heavy metal ions rejection ratio and adsorption capacity of membrane were also improved with the addition of A-HNTs. More importantly, A-HNTs@PVDFmembrane exhibited excellent rejection stability and reuse performances after several times fouling and washing tests. It can be expected that the present work will provide insight into a new method for membrane modification in the field of wastewater treatment. PMID:27262273

Geostatistical data analysis techniques were used to stochastically model the spatial variability of groundwater pore velocity in a potential waste repository site. Kriging algorithms were applied to Hanford Reservation data to estimate hydraulic conductivities, hydraulic head gradients, and pore velocities. A first-order Taylor series expansion for pore velocity was used to statistically combine hydraulic conductivity, hydraulic head gradient, and effective porosity surfaces and uncertainties to characterize the pore velocity uncertainty. Use of these techniques permits the estimation of pore velocity uncertainties when pore velocity measurements do not exist. Large pore velocity estimation uncertainties were found to be located in the region where the hydraulic head gradient relative uncertainty was maximal.

Curcumin is a polyphenol derived from turmeric with recognized antioxidant properties. Hexavalent chromium is an environmental toxic and carcinogen compound that induces oxidative stress. The objective of this study was to evaluate the potential protective effect of curcumin on the hepatic damage generated by potassium dichromate (K2Cr2O7) in rats. Animals were pretreated daily by 9-10 days with curcumin (400 mg/kg b.w.) before the injection of a single intraperitoneal of K2Cr2O7 (15 mg/kg b.w.). Groups of animals were sacrificed 24 and 48 h later. K2Cr2O7-induced damage to the liver was evident by histological alterations and increase in the liver weight and in the activity of alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, and alkaline phosphatase in plasma. In addition, K2Cr2O7 induced oxidative damage in liver and isolated mitochondria, which was evident by the increase in the content of malondialdehyde and protein carbonyl and decrease in the glutathione content and in the activity of several antioxidant enzymes. Moreover, K2Cr2O7 induced decrease in mitochondrial oxygen consumption, in the activity of respiratory complex I, and permeability transition pore opening. All the above-mentioned alterations were prevented by curcumin pretreatment. The beneficial effects of curcumin against K2Cr2O7-induced liver oxidative damage were associated with prevention of mitochondrial dysfunction. PMID:23956771

Micro- and nano-fabrication methods facilitate the use of nanostructures for the separation of collections of particles and nanobio-based optical and electrochemical sensing. We have presented an easy and simple nanopore size reduction method of a low-stressed silicon nitride (SiN) membrane nanosieve (100×100 μm2) using a nanoimprinting method based on a natural thermal reflow of the contact imprinting polymer, possibly maintaining compatibility with complementary metal-oxide semiconductor integrated circuit processes. The nanopore pattern size of this nanosieve membrane was precisely patterned by a nanoimprinting process using an electron beam patterned silicon master, to about 30-nm diameter. By employing mainly an electron beam resist reflow phenomena after a nanoimprinting process and anisotropic reactive ion etch, the etch holes' size was fabricated to be the same with nanopatterns on the polymer. The contact imprinting master can be used continually for the generation of nanopore patterns simply and easily. It can endure harsh conditions like high temperature up to 800°C, and it is inert to many aggressive and strong chemicals. Also, this would be a low-cost, simple, and easy fabrication method for the precise and reliable size-reduction control of nanopores for mass production of nanobio sensors or chips. PMID:24503699

Micro- and nano-fabrication methods facilitate the use of nanostructures for the separation of collections of particles and nanobio-based optical and electrochemical sensing. We have presented an easy and simple nanopore size reduction method of a low-stressed silicon nitride (SiN) membrane nanosieve (100×100 μ) using a nanoimprinting method based on a natural thermal reflow of the contact imprinting polymer, possibly maintaining compatibility with complementary metal-oxide semiconductor integrated circuit processes. The nanopore pattern size of this nanosieve membrane was precisely patterned by a nanoimprinting process using an electron beam patterned silicon master, to about 30-nm diameter. By employing mainly an electron beam resist reflow phenomena after a nanoimprinting process and anisotropic reactive ion etch, the etch holes' size was fabricated to be the same with nanopatterns on the polymer. The contact imprinting master can be used continually for the generation of nanopore patterns simply and easily. It can endure harsh conditions like high temperature up to 800°C, and it is inert to many aggressive and strong chemicals. Also, this would be a low-cost, simple, and easy fabrication method for the precise and reliable size-reduction control of nanopores for mass production of nanobio sensors or chips.

Lithium-ion batteries have been widely used in electronic devices including mobile phones, laptop computers, and cameras due to their high specific energy, high energy density, long cycling lifetime, and low self-discharge rate. Nowadays, lithium-ion batteries are finding new applications in electric/hybrid vehicles and energy storage for smart grids. To be used in these new applications, novel battery components are needed so that lithiumion batteries with higher cell performance, better safety, and lower cost can be developed. A separator is an important component to obtain safe batteries and its primary function is to prevent electronic contact between electrodes while regulating cell kinetics and ionic flow. Currently, microporous membranes are the most commonly used separator type and they have good mechanical properties and chemical stability. However, their wettability and thermal stabilities are not sufficient for applications that require high operating temperature and high performance. Due to the superior properties such as large specific surface area, small pore size and high porosity, electrospun nanofiber membranes can be good separator candidate for highperformance lithium-ion batteries. In this work, we focus our research on fabricating nanofiber-based membranes to design new high-performance separators with good thermal stability, as well as superior electrochemical performance compared to microporous polyolefin membranes. To combine the good mechanical strength of PP nonwovens with the excellent electrochemical properties of SiO2/polyvinylidene fluoride (PVDF) composite nanofibers, SiO 2/PVDF composite nanofiber-coated PP nonwoven membranes were prepared. It was found that the addition of SiO2 nanoparticles played an important role in improving the overall performance of these nanofiber-coated nonwoven membranes. Although ceramic/polymer composites can be prepared by encapsulating ceramic particles directly into polymer nanofibers, the performance

Thin polymer films have been identified as one of the major enabling technologies for future space-based systems. Potential devices include those based on piezoelectric bimorph polymers that deform when a charge is deposited, for example, from an electron gun. The thin-film and lightweight nature of the polymeric devices will allow them to be launched more readily and deployed to operating conditions once in orbit. Until now little work has been done aimed at investigating the performance of piezoelectric properties of PVDF and its copolymers and the prediction of their long-term stability in low Earth orbit (LEO) environmental conditions. In this paper, the piezoelectric properties of PVDF and the copolymers formed from polymerization of vinylidene fluoride and trifluoroethylene (TrFE) or hexafluoropropylene (HFP) have been studied over a broad temperature range simulating that expected in LEO. The temperatures experienced by unprotected polymers on low altitude spacecraft have previously been reported as ranging from approximately -100 C to +130 C as the polymer/spacecraft passes in and out of the Earth's shadow. To examine the effects of temperature on the piezoelectric properties of poled PVDF, P(VDF-TrFE) and P(VDF-HFP) the d{sub 33} piezoelectric coefficients and electric displacement-electric field (D-E) hysteresis loops were measured up to 160 C for the d{sub 33} measurements and from -80 to +110 C for the D-E loops. The room temperature d{sub 33} coefficient of PVDF homopolymer films, annealed for extended periods at 50, 80 and 125 C, dropped rapidly within a few days of heating, then remained unchanged for periods of up to 300 days. In contrast, the TrFE copolymer exhibited greater thermal stability than the homopolymer, with the d{sub 33} remaining almost unchanged from the pre-annealing value after heating at 50, 80 and 125 C. The HFP copolymer exhibited poor retention of d33 at temperatures above 80 C. For all three polymers short term annealing at 160

In this paper, a PVDF film sensor was used to measure the transient responses of a cantilever beam subjected to an impact loading. The measurement capability of a PVDF sensor is affected by the area of the PVDF film sensor and the signal conditioner (charge amplifier). The influences of these effects on the experimental measurements were investigated. The transient responses for the dynamic strain of the beam were measured simultaneously by the PVDF sensor and a conventional strain gauge. The resonant frequencies of the beam were determined by applying the Fast Fourier Transform on transient results in the time domain of the PVDF sensor and the strain gauge. The experimentally measured resonant frequencies from the PVDF sensor and the strain gauge were compared with those predicted from theoretical and FEM numerical calculations. Based on the comparison of the results measured for these two sensors, the PVDF film sensor proved capable of measuring transient responses for dynamic strain, and its sensitivity is better than that of the strain gauge. Furthermore, almost all the resonant frequencies can be obtained from the results of transient responses for PVDF film. PMID:22438754

Cell-penetrating and antimicrobial peptides show remarkable ability to translocate across physiological membranes. Along with factors such as electric potential induced-perturbations of membrane structure and surface tension effects, experiments invoke pore-like membrane configurations during the solute transfer process into vesicles and cells. The initiation and formation of pores are associated with a non-trivial free energy cost, thus necessitating consideration of the factors associated with pore formation and attendant free energetics. Due to experimental and modeling challenges related to the long timescales of the translocation process, we use umbrella-sampling molecular dynamics simulations with a lipid-density based order parameter to investigate membranepore-formation free energy employing Martini coarse-grained models. We investigate structure and thermodynamic features of the pore in 18 lipids spanning a range of head-groups, charge states, acyl chain lengths and saturation. We probe the dependence of pore-formation barriers on area per lipid, lipid bilayer thickness, membrane bending rigidities in three different lipid classes. The pore formation free energy in pure bilayers and peptide translocating scenarios are significantly coupled with bilayer thickness. Thicker bilayers require more reversible work to create pores. Pore formation free energy is higher in peptide-lipid systems relative to the peptide-free lipid systems due to penalties to maintain solvation of charged hydrophilic solutes within the membrane environment. PMID:25614183

Living cells regulate the activity of their ion channels through a process known as gating. To open the pore, protein conformational changes must occur within a channel's membrane-spanning ion pathway. KcsA and MthK, closed and opened K+ channels, respectively, reveal how such gating transitions occur. Pore-lining `inner' helices contain a `gating hinge' that bends by approximately 30°. In a straight conformation four inner helices form a bundle, closing the pore near its intracellular surface. In a bent configuration the inner helices splay open creating a wide (12Å) entryway. Amino-acid sequence conservation suggests a common structural basis for gating in a wide range of K+ channels, both ligand- and voltage-gated. The open conformation favours high conduction by compressing the membrane field to the selectivity filter, and also permits large organic cations and inactivation peptides to enter the pore from the intracellular solution.

Polyvinylidene fluoride (PDVF), one of the best electrically active polymer material & an interesting candidate to address the electrical control of its functional properties like ferroelectricity, piezoelectricity, pyroelectricity etc. In the current work, with the help of spin coater and DC magnetron sputtering techniques, semi-crystallized PVDF thin films prominent in alpha phase is prepared in capacitor like structure and their electrical characterization is emphasized. In current-voltage (I-V) and resistance-voltage (R-V) measurements, clear nonlinearity and resistance switching has been observed for films prepared using 7 wt% 2-butanone and 7 wt% Dimethyl Sulfoxide (DMSO) solvents.

The purpose of this project was to do some preliminary studies and process development on electroactive polymers to be used for tunable optical elements and MEMS actuators. Working in collaboration between Sandia National Labs and The University of Illinois Urbana-Champaign, we have successfully developed a process for applying thin films of poly (vinylidene fluoride) (PVDF) onto glass substrates and patterning these using a novel stamping technique. We observed actuation in these structures in static and dynamic measurements. Further work is needed to characterize the impact that this approach could have on the field of tunable optical devices for sensing and communication.

This paper examines phase transitions in cerium during shock compression using PVDF gauges. A two-wave structure was observed with loading pressures of 4GPa - 12GPa. The wave structure consists of leading isentropic compression wave followed by a shock wave. This wave structure was formed as a result of the isomorphic (γ-α) phase transition. The wave profiles exhibited no peculiarities resulting from the polymorphic transition (α-ɛ) as predicted by Elkin et. al [Proceedings of the International Conference VII Khariton Readings, Sarov 2005, p. 116].

The current status of the University of Chicago Polyvinylidene Fluoride (PVDF) flux/mass/velocity/trajectory instrumentation is summarized. The particle response and thermal stability characteristics of pure PVDF and PVDF copolymer sensors are described, as well as the characteristics of specially constructed two-dimensional position-sensing PVDF sensors. The performance of high-flux systems and of velocity/trajectory systems using these sensors is discussed, and the objectives and designs of a PVDF velocity/trajectory dust instrument for launch on the Advanced Research and Global Observation Satellite (ARGOS) in 1995 and of a high-flux dust instrument for launch on the Cassini spacecraft to Saturn in 1997 are summarized.

Several methods are disclosed for the preparation microporous alumina ceramic membranes. For the first time, porous alumina membranes are made which have mean pore sizes less than 100 Angstroms and substantially no pores larger than that size. The methods are based on improved sol-gel techniques.

Several methods are disclosed for the preparation microporous alumina ceramic membranes. For the first time, porous alumina membranes are made which have mean pore sizes less than 100 Angstroms and substantially no pores larger than that size. The methods are based on improved sol-gel techniques.

Due to their ultra lightweight and high packaging efficiency, membrane reflectors are getting more and more attentions for mission architectures that need extremely large inspace deployable antennas. However how to maintain the surface shape of a membrane reflector to the instrument precision requirements is a very challenging problem. This experimental study investigated using PVDFmembrane piezoelectric material as actuators to control the surface figures of membrane reflectors. The feasibility of this approach is demonstrated by several sets of test results.

Poly(vinylidene fluoride) (PVDF) membranes were prepared by non solvent induced phase separation (NIPS), melt spinning and the solution-cast method. The effect of preparation methods with different membrane formation mechanisms on crystallization behavior and tensile strength of PVDFmembranes was investigated. Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and X-ray diffraction (XRD) were employed to examine the crystal form of the surface layers and the overall membranes, respectively. Spherulite morphologies and thermal behavior of the membranes were studied by polarized light optical microscopy (PLO) and differential scanning calorimetry (DSC) separately. It was found that the crystallization behavior of PVDFmembranes was closely related to the preparation methods. For membranes prepared by the NIPS method, the skin layers had a mixture of α and β phases, the overall membranes were predominantly α phase, and the total crystallinity was 60.0% with no spherulite. For melt spinning membranes, the surface layers also showed a mixture of α and β phases, the overall membranes were predominantly α phase. The total crystallinity was 48.7% with perfect spherulites. Whereas the crystallization behavior of solution-cast membranes was related to the evaporation temperature and the additive, when the evaporation temperature was 140 °C with a soluble additive in the dope solution, obvious spherulites appeared. The crystalline morphology of PVDF exerted a great influence on the tensile strength of the membranes, which was much higher with perfect spherulites. PMID:24957064

Poly(vinylidene fluoride) (PVDF) membranes were prepared by non solvent induced phase separation (NIPS), melt spinning and the solution-cast method. The effect of preparation methods with different membrane formation mechanisms on crystallization behavior and tensile strength of PVDFmembranes was investigated. Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and X-ray diffraction (XRD) were employed to examine the crystal form of the surface layers and the overall membranes, respectively. Spherulite morphologies and thermal behavior of the membranes were studied by polarized light optical microscopy (PLO) and differential scanning calorimetry (DSC) separately. It was found that the crystallization behavior of PVDFmembranes was closely related to the preparation methods. For membranes prepared by the NIPS method, the skin layers had a mixture of α and β phases, the overall membranes were predominantly α phase, and the total crystallinity was 60.0% with no spherulite. For melt spinning membranes, the surface layers also showed a mixture of α and β phases, the overall membranes were predominantly α phase. The total crystallinity was 48.7% with perfect spherulites. Whereas the crystallization behavior of solution-cast membranes was related to the evaporation temperature and the additive, when the evaporation temperature was 140 °C with a soluble additive in the dope solution, obvious spherulites appeared. The crystalline morphology of PVDF exerted a great influence on the tensile strength of the membranes, which was much higher with perfect spherulites. PMID:24957064

We develop sustainable anti-biofouling ultrafiltration membrane nanocomposites by covalently immobilizing silver nanoparticles (AgNPs) onto poly(vinylidene fluoride) (PVDF) membrane mediated by a thiol-end functional amphiphilic block copolymer linker. Field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDXS) measurements reveal that the AgNPs are highly bound and dispersed to the PVDFmembrane due to the strong affinity of the AgNPs with the thiol-modified block copolymeric linkers, which have been anchored to the PVDFmembrane. The membrane performs well under water permeability and particle rejection measurements, despite the high deposition of AgNPs on the surface of membrane. The Ag-PVDFmembrane nanocomposite significantly inhibits the growth of bacteria on the membrane surface, resulting in enhanced anti-biofouling property. Importantly, the AgNPs are not released from the membrane surface due to the robust covalent bond between the AgNPs and the thiolated PVDFmembrane. The stability of the membrane nanocomposite ensures a sustainable anti-biofouling activity of the membrane. PMID:24144007

Proteinaceous nanometer-scale pores are ubiquitous in biology. The canonical ionic channels (e.g., those that transport Na(+), K(+), Ca(2+), and Cl(-) across cell membranes) play key roles in many cellular processes, including nerve and muscle activity. Another class of channels includes bacterial pore-forming toxins, which disrupt cell function, and can lead to cell death. We describe here the recent development of these toxins for a wide range of biological sensing applications. This article is part of a Special Issue entitled: Pore-Forming Toxins edited by Mauro Dalla Serra and Franco Gambale. PMID:26431785

Cellular membranes separate distinct aqueous compartments, but can be breached by transient hydrophilic pores. A large energetic cost prevents pore formation, which is largely dependent on the composition and structure of the lipid bilayer. The softness of bilayers and the disordered structure of pores make their characterization difficult. We use molecular-dynamics simulations with atomistic detail to study the thermodynamics, kinetics, and mechanism of pore formation and closure in DLPC, DMPC, and DPPC bilayers, with pore formation free energies of 17, 45, and 78 kJ/mol, respectively. By using atomistic computer simulations, we are able to determine not only the free energy for pore formation, but also the enthalpy and entropy, which yields what is believed to be significant new insights in the molecular driving forces behind membrane defects. The free energy cost for pore formation is due to a large unfavorable entropic contribution and a favorable change in enthalpy. Changes in hydrogen bonding patterns occur, with increased lipid-water interactions, and fewer water-water hydrogen bonds, but the total number of overall hydrogen bonds is constant. Equilibrium pore formation is directly observed in the thin DLPC lipid bilayer. Multiple long timescale simulations of pore closure are used to predict pore lifetimes. Our results are important for biological applications, including the activity of antimicrobial peptides and a better understanding of membrane protein folding, and improve our understanding of the fundamental physicochemical nature of membranes. PMID:24411253

Simultaneous removal of two heavy metals, lead(II) and cadmium(II), from mixed feed using supported liquid membrane (SLM) based technique is investigated in this work. The carrier-solvent combination of "sodium salt of Di-2-ethylhexylphosphoric acid (D2EHPA) (4% w/w) in environmentally benign coconut oil" was immobilized into the pores of solid polymeric polyvinylidene fluoride (PVDF) support. Sodium carbonate (Na2CO3) was used as the stripping agent. Carbonate salts of lead(II) and cadmium(II) were formed in the stripping side interface and they were insoluble in water leading to precipitation inside the stripping solution. The transportation of solute is positively affected due to the precipitation. Lead(II) removal was found to be preferential due to its favorable electronic configuration. The conversion of the liquid waste to the solid one was added advantage for the final removal of hazardous heavy metals. PMID:26252994

A study of mechanisms of electrotransfection using Escherichia coli (JM 105) and the plasmid DNA pBR322 as model system is reported. pBR322 DNA carries an ampicillin resistance gene: E. coli transformants are conveniently assayed by counting colonies in a selection medium containing 50 micrograms/ml ampicillin and 25 micrograms/ml streptomycin. Samples not exposed to the electric field showed no transfection. In the absence of added cations, the plasmid DNA remains in solution and the efficiency of the transfection was 2 x 10(6)/micrograms DNA for cells treated with a 8-kV/cm, 1-ms electric pulse (square wave). DNA binding to the cell membrane greatly enhanced the efficiency of the transfection and this binding was increased by milimolar concentrations of CaCl2, MgCl2, or NaCl (CaCl2 greater than MgCl2 greater than NaCl). For example, in the presence of 2.5 mM CaCl2, 55% of the DNA added bound to E. coli and the transfection efficiency was elevated by two orders of magnitude (2 x 10(8)/micrograms DNA). These ions did not cause cell aggregation. With a low ratio of DNA to cells (less than 1 copy/cell), transfection efficiency correlated with the amount of DNA bound to the cell surface irrespective of salts. When the DNA binding ratio approached zero, the transfection efficiency was reduced by two to three orders, indicating that DNA entry by diffusion through the bulk solution was less than 1%. Square pulses of up to 12 kV/cm and 1 ms were used in the electrotransfection experiments.

Identification of Treponema pallidum rare outer membrane proteins (OMPs) has been a longstanding objective of syphilis researchers. We recently developed a consensus computational framework that employs a battery of cellular localization and topological prediction tools to generate ranked clusters of candidate rare OMPs (D. L. Cox et al., Infect. Immun. 78:5178–5194, 2010). TP0117/TP0131 (TprC/D), a member of the T. pallidum repeat (Tpr) family, was a highly ranked candidate. Circular dichroism, heat modifiability by SDS-PAGE, Triton X-114 phase partitioning, and liposome incorporation confirmed that full-length, recombinant TprC (TprCFl) forms a β-barrel capable of integrating into lipid bilayers. Moreover, TprCFl increased efflux of terbium-dipicolinic acid complex from large unilamellar vesicles and migrated as a trimer by blue-native PAGE. We found that in T. pallidum, TprC is heat modifiable, trimeric, expressed in low abundance, and, based on proteinase K accessibility and opsonophagocytosis assays, surface exposed. From these collective data, we conclude that TprC is a bona fide rare OMP as well as a functional ortholog of Escherichia coli OmpF. We also discovered that TprC has a bipartite architecture consisting of a soluble N-terminal portion (TprCN), presumably periplasmic and bound directly or indirectly to peptidoglycan, and a C-terminal β-barrel (TprCC). Syphilitic rabbits generate antibodies exclusively against TprCC, while secondary syphilis patients fail to mount a detectable antibody response against either domain. The syphilis spirochete appears to have resolved a fundamental dilemma arising from its extracellular lifestyle, namely, how to enhance OM permeability without increasing its vulnerability to the antibody-mediated defenses of its natural human host. PMID:22389487

The characteristics of Lamb waves, which are multimodal and dispersive, provide both challenges and opportunities for structural health monitoring (SHM). Methods for nondestructive testing with Lamb waves are well established. For example, mode content can be determined by moving a sensor to different positions and then transforming the spatial-temporal data into the wavenumber-frequency domain. This mode content information is very useful because at every frequency each mode has a unique wavestructure, which is largely responsible for its sensitivity to material damage. Furthermore, mode conversion occurs when the waves interact with damage, making mode content an excellent damage detection feature. However, in SHM, the transducers are typically at fixed locations and are immovable. Here, an affixed polyvinylidene fluoride (PVDF) multielement sensor is shown to provide these same capabilities. The PVDF sensor is bonded directly to the waveguide surface, conforms to curved surfaces, has low mass, low profile, low cost, and minimal influence on passing Lamb waves. While the mode receivability is dictated by the sensor being located on the surface of the waveguide, both symmetric and antisymmetric modes can be detected and group velocities measured. PMID:26540682

This paper describes a new type of contact vibration sensor made by bonding piezoelectric PVDF film to a curved frame structure. The concave surface of the film is bonded to a rubber piece having a front contact face. Vibration is transmitted from this face through the rubber to the surface of the PVDF film. Pressure normal to the surface of the film is converted to circumferential strain, and an electric field is induced by the piezoelectric effect. The frequency response of the device was measured using an accelerometer mounted between the rubber face and a rigid vibration exciter plate. Sensitivity (voltage per unit displacement) was deduced from the device output and measured acceleration. The sensitivity was flat from 16 Hz to 3 kHz, peaking at 6 kHz due to a structural resonance. Calculations predicting performance against human tissue (stethoscope or contact microphone) show results similar to data measured against the metal vibrator. This implies that an accelerometer can be used for calibrating a stethoscope or contact microphone. The observed arterial pulse waveform showed more low-frequency content than a conventional electronic stethoscope.

Piezoelectric polymers based on polyvinylidene fluoride (PVDF) are of interest for large aperture space-based telescopes. Dimensional adjustments of adaptive polymer films are achieved via charge deposition and require a detailed understanding of the piezoelectric material responses which are expected to suffer due to strong vacuum UV, gamma, X-ray, energetic particles and atomic oxygen under low earth orbit exposure conditions. The degradation of PVDF and its copolymers under various stress environments has been investigated. Initial radiation aging studies using gamma- and e-beam irradiation have shown complex material changes with significant crosslinking, lowered melting and Curie points (where observable), effects on crystallinity, but little influence on overall piezoelectric properties. Surprisingly, complex aging processes have also been observed in elevated temperature environments with annealing phenomena and cyclic stresses resulting in thermal depoling of domains. Overall materials performance appears to be governed by a combination of chemical and physical degradation processes. Molecular changes are primarily induced via radiative damage, and physical damage from temperature and AO exposure is evident as depoling and surface erosion. Major differences between individual copolymers have been observed providing feedback on material selection strategies.

BaTiO3 nanoparticles (from Nanostructured & Amorphous Materials, Inc.) were dispersed within PVDF powder (from Sigma Aldrich) by melt mixing using a Haake Rheomix with two counter rotating screws. The mixing consisted of 3 segments first at 190 °C and 60 rotations per minute (rpm) for 30 minutes, second at 210 °C and 80 rpm for 15 minutes, and the last at 180 °C and 60 rpm for 30 minutes. Nanocomposites containing various fractions of nanofiller, ranging from 0 to 15 % wt. have been prepared. Raman investigations on the as obtained nanocomposites have been performed by using a Renishaw InVia spectrometer operating at 532 and 785 cm-1. Complementary Wide Angle X-Ray Scattering measurements on the same samples revealed that the as obtained nanocomposites have a dominant beta phase and provided additional information about the size of polymeric crystallites. The effect of the nanofiller on the Raman lines of the PVDF are analyzed in detail. The Raman spectra have been deconvoluted assuming a superposition distorted Lorentzian line shape. The changes of the Raman spectrum parameters (position, amplitude, width, and asymmetry factors) due to the loading with BaTiO3 is discussed.

A nanoporous catalytic membrane which displays several unique features Including pores which can go through the entire thickness of the membrane. The membrane has a higher catalytic and product selectivity than conventional catalysts. Anodic aluminum oxide (AAO) membranes serve as the catalyst substrate. This substrate is then subjected to Atomic Layer Deposition (ALD), which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate by deposition of a preparatory material. Subsequent deposition of a catalytic layer on the inner surfaces of the pores reduces pore sizes to less than 10 nm and allows for a higher degree of reaction selectivity. The small pore sizes allow control over which molecules enter the pores, and the flow-through feature can allow for partial oxidation of reactant species as opposed to complete oxidation. A nanoporous separation membrane, produced by ALD is also provided for use in gaseous and liquid separations. The membrane has a high flow rate of material with 100% selectivity. Also provided is a method for producing a catalytic membrane having flow-through pores and discreet catalytic clusters adhering to the inside surfaces of the pores.

We report Ag nanoparticle induced Electromagnetic Interference (EMI) shielding in a flexible composite films of Ag nanoparticles incorporated graphite/poly-vinylidene difluoride (PVDF). PVDF nanocomposite thin-films were synthesized by intercalating Ag in Graphite (GIC) followed by dispersing GIC in PVDF. The X-ray diffraction analysis and the high-resolution transmission electron microscope clearly dictate the microstructure of silver nanoparticles in graphite intercalated composite of PVDF matrix. The conductivity values of nanocomposites are increased upto 2.5 times when compared to neat PVDF having a value of 2.70 S/cm at 1 MHz. The presence of Ag broadly enhanced the dielectric constant and lowers the dielectric loss of PVDF matrix proportional to Ag content. The EMI shielding effectiveness of the composites is 29.1 dB at 12.4 GHz for the sample having 5 wt. % Ag and 10 wt. % graphite in PVDF.

Ultrasonic strain sensing performance of the large area PVDF with Inter Digital Electrodes (IDE) is studied in this work. Procedure to obtain IDE on a beta-phase PVDF is explained. PVDF film with IDE is bonded on a plate structure and is characterized for its directional sensitivity at different frequencies. Guided waves are induced on the IDE-PVDF sensor from different directions by placing a piezoelectric wafer actuator at different angles. Strain induced on the IDE-PVDF sensor by the guided waves in estimated by using a Laser Doppler Vibrometer (LDV) and a wave propagation model. Using measured voltage response from IDE-PVDF sensor and the strain measurements from LDV the piezoelectric coefficient is estimated in various directions. The variation of ℯ11 e at different angles shows directional sensitivity of the IDE-PVDF sensor to the incident guided waves. The present study provides an effective technique to characterize thin film piezoelectric sensors for ultrasonic strain sensing at very high frequencies of 200 kHz. Often frequency of the guided wave is changed to alter the wavelength to interrogate damages of different sizes in Structural Health Monitoring (SHM) applications. The unique property of directional sensitivity combined with frequency tunability makes the IDEPVDF sensor most suitable for SHM of structures.

Nano composites of PVDF with ionic liquid [EMIM][TF2N] (IL) modified MWNTs were prepared by melt blending to design materials for EMI shielding applications. MWNTs and IL were mixed in two different ratios (1:1 and 1:5) to facilitate better dispersion of MWNTs in PVDF. It was observed that non-covalent interactions between IL and PVDF resulted in a better dispersion of CNTs and was consistent with increasing concentration of IL. Interestingly, IL modified MWNTs induced the formation of γ-phase crystals in PVDF, which was further confirmed by XRD, FTIR and DSC. Melt rheological measurements and DSC analysis revealed the plasticization effect of IL in PVDF composites further manifesting in a decrease in the storage modulus and the glass transition temperature. This phenomenal effect presumably led to better dispersion of IL modified MWNTs in PVDF further resulting in a significant improvement in electrical conductivity and structural properties. More interestingly, the elongational properties in the composites improved with IL modified MWNTs in striking contrast to MWNT filled PVDF composites. The ac conductivity of the composites reached about 10-3 S cm-1 with the addition of 2 wt% IL modified MWNTs (1:1). This further led to a high electro-magnetic interference (EMI) shielding effectiveness of about 20 dB at 2 wt% IL modified MWNTs. Such materials can further be explored for flexible, lightweight EMI shielding materials for a wide range of operating frequency.

Neurotransmitter release is mediated by the SNARE proteins synaptobrevin II (sybII, also known as VAMP2), syntaxin, and SNAP-25, generating a force transfer to the membranes and inducing fusion pore formation. However, the molecular mechanism by which this force leads to opening of a fusion pore remains elusive. Here we show that the ability of sybII to support exocytosis is inhibited by addition of one or two residues to the sybII C terminus depending on their energy of transfer from water to the membrane interface, following a Boltzmann distribution. These results suggest that following stimulation, the SNARE complex pulls the C terminus of sybII deeper into the vesicle membrane. We propose that this movement disrupts the vesicular membrane continuity leading to fusion pore formation. In contrast to current models, the experiments suggest that fusion pore formation begins with molecular rearrangements at the intravesicular membrane leaflet and not between the apposed cytoplasmic leaflets. PMID:20937897

Supported inorganic membranes capable of molecular sieving, and methods for their production, are provided. The subject membranes exhibit high flux and high selectivity. The subject membranes are substantially defect free and less than about 100 nm thick. The pores of the subject membranes have an average critical pore radius of less than about 5 .ANG., and have a narrow pore size distribution. The subject membranes are prepared by coating a porous substrate with a polymeric sol, preferably under conditions of low relative pressure of the liquid constituents of the sol. The coated substrate is dried and calcined to produce the subject supported membrane. Also provided are methods of derivatizing the surface of supported inorganic membranes with metal alkoxides. The subject membranes find use in a variety of applications, such as the separation of constituents of gaseous streams, as catalysts and catalyst supports, and the like.

This paper reports a systematic optimization of processing conditions of PVDF-TrFE piezoelectric thin films, used as integrated transducers in organic MEMS resonators. Indeed, despite data on electromechanical properties of PVDF found in the literature, optimized processing conditions that lead to these properties remain only partially described. In this work, a rigorous optimization of parameters enabling state-of-the-art piezoelectric properties of PVDF-TrFE thin films has been performed via the evaluation of the actuation performance of MEMS resonators. Conditions such as annealing duration, poling field and poling duration have been optimized and repeatability of the process has been demonstrated. PMID:26792224

This paper reports a systematic optimization of processing conditions of PVDF-TrFE piezoelectric thin films, used as integrated transducers in organic MEMS resonators. Indeed, despite data on electromechanical properties of PVDF found in the literature, optimized processing conditions that lead to these properties remain only partially described. In this work, a rigorous optimization of parameters enabling state-of-the-art piezoelectric properties of PVDF-TrFE thin films has been performed via the evaluation of the actuation performance of MEMS resonators. Conditions such as annealing duration, poling field and poling duration have been optimized and repeatability of the process has been demonstrated. PMID:26792224

Mechanical properties of the thin film piezoelectric polymer PVDF are examined experimentally. The developed program comprising static, creep and dynamic (oscillatory) tests provides a consistent empirical data base for material characterization of the polymer: The results of the study indicate that PVDF thin films are orthotropic materials. The constitutive equations of linear hereditary viscoelasticity are shown to accurately represent the time-dependent response of PVDF over a wide range of stresses, temperatures and frequencies. The experiments indicate that the polymer exhibits thermorheologically simple behavior governed by the temperature-frequency correspondence principle.

This paper reports a systematic optimization of processing conditions of PVDF-TrFE piezoelectric thin films, used as integrated transducers in organic MEMS resonators. Indeed, despite data on electromechanical properties of PVDF found in the literature, optimized processing conditions that lead to these properties remain only partially described. In this work, a rigorous optimization of parameters enabling state-of-the-art piezoelectric properties of PVDF-TrFE thin films has been performed via the evaluation of the actuation performance of MEMS resonators. Conditions such as annealing duration, poling field and poling duration have been optimized and repeatability of the process has been demonstrated.

Hydrophilic pores are formed in peptide free lipid bilayers under mechanical stress. It has been proposed that the transport of ionic species across such membranes is largely determined by the existence of such meta-stable hydrophilic pores. To study the properties of these structures and understand the mechanism by which pore expansion leads to membrane rupture, a series of molecular dynamics simulations of a dipalmitoylphosphatidylcholine (DPPC) bilayer have been conducted. The system was simulated in two different states; first, as a bilayer containing a meta-stable pore and second, as an equilibrated bilayer without a pore. Surface tension in both cases was applied to study the formation and stability of hydrophilic pores inside the bilayers. It is observed that below a critical threshold tension of ∼38 mN/m the pores are stabilized. The minimum radius at which a pore can be stabilized is 0.7 nm. Based on the critical threshold tension the line tension of the bilayer was estimated to be ∼3 × 10−11 N, in good agreement with experimental measurements. The flux of water molecules through these stabilized pores was analyzed, and the structure and size of the pores characterized. When the lateral pressure exceeds the threshold tension, the pores become unstable and start to expand causing the rupture of the membrane. In the simulations the mechanical threshold tension necessary to cause rupture of the membrane on a nanosecond timescale is much higher in the case of the equilibrated bilayers, as compared with membranes containing preexisting pores. PMID:15041656

We have used PVDF gauges to determine time-resolved stresses resulting from interaction between hypervelocity-impact-generated debris clouds and various target gauge blocks. Debris clouds were generated from three different impact configurations: (1) steel spheres impacting steel bumper sheets at 4.5 to 6.0 km/s, (2) aluminum inhibited shaped-charge jets impacting aluminum bumper sheets at 11.4 km/s, and (3) titanium disks impacting titanium bumper sheets at 7.6 to 10.1 km/s. Additional data were collected from the various experiments using flash X-ray radiography, pulsed laser photography, impact flash measurements, time-resolved strain gauge measurements, and velocity interferometry (VISAR). Data from these various techniques are in general agreement with one another and with hydrocode predictions, and provide a quantitative and comprehensive picture of impact-generated debris clouds.

The ATP-gated P2X7R (P2X7R) is a channel, which is involved in events, such as inflammation, cell death, and pain. The most intriguing event concerning P2X7R functions is the phenomenon of pore dilation. Once P2X7R is activated, the permeability of the plasma membrane becomes higher, leading to the permeation of 1000 Da-weight solutes. The mechanisms involved in this process remain unclear. Nevertheless, this event is not exclusively through P2X7R, as other proteins may form large pores in the plasma membrane. Recent evidence concerning pore formation reveals putative P2X7R and other pores-associated protein complexes, revealing cross-interactive pharmacological and biophysical issues. In this work, we showed results that corroborated with cross-interactive aspects with P2X7R and pores in astrocytes. These cells expressed most of the pores, including P2X7R. We discovered that different pore types open with peculiar characteristics, as both anionic and cationic charged solutes permeate the plasma membrane, following P2X7R activation. Moreover, we showed that both synergic and additive relationships are found within P2X7, cationic, and anionic large pores. Therefore, our data suggest that other protein-related pores are assembled following the formation of P2X7R pore. PMID:26830892

Melittin has been reported to form toroidal pores under certain conditions, but the atomic-resolution structure of these pores is unknown. A 9-μs all-atom molecular-dynamics simulation starting from a closely packed transmembrane melittin tetramer in DMPC shows formation of a toroidal pore after 1 μs. The pore remains stable with a roughly constant radius for the rest of the simulation. Surprisingly, one or two melittin monomers frequently transition between transmembrane and surface states. All four peptides are largely helical. A simulation in a DMPC/DMPG membrane did not lead to a stable pore, consistent with the experimentally observed lower activity of melittin on anionic membranes. The picture that emerges from this work is rather close to the classical toroidal pore, but more dynamic with respect to the configuration of the peptides. PMID:25992720

This work explores the structural phase studies of organic polymer- polyvinylidene fluoride (PVDF) thin films in semi-crystallized phase and nano-patterned PVDF thin films. The nanopatterns are transferred with the CD layer as a master using soft lithography technique. The semi-crystalline PVDF films were prepared by a still and hot (SH) method, using a homemade spin coater that has the proficiency of substrate heating by a halogen lamp. Using this set up, smooth PVDF thin films in semi-crystalline α-phase were prepared using 2-Butanone as solvent. XRD, AFM and confocal Raman microscope have been utilized to study the structural phase, crystallinity and quality of the films.

This work explores the structural phase studies of organic polymer- polyvinylidene fluoride (PVDF) thin films in semi-crystallized phase and nano-patterned PVDF thin films. The nanopatterns are transferred with the CD layer as a master using soft lithography technique. The semi-crystalline PVDF films were prepared by a still and hot (SH) method, using a homemade spin coater that has the proficiency of substrate heating by a halogen lamp. Using this set up, smooth PVDF thin films in semi-crystalline α-phase were prepared using 2-Butanone as solvent. XRD, AFM & confocal Raman microscope have been utilized to study the structural phase, crystallinity and quality of the films.

To track prey or avoid predators, many arthropods can detect variations in airflow and pressure gradients using an array of very thin and sensitive filiform hairs. In this study, metal core piezoelectric poly(vinylidene fluoride) (PVDF) fibers were prepared to mimic such hair sensors. The flexibility of the fibers was very good, which was helpful for overcoming the typical brittleness of piezoelectric ceramic fibers. At the same time, the diameter of the fibers was very small (down to 50 μm in diameter). In order to mimic the insects’ hairs to the maximum extent, which was expected to greatly improve the sensitivity of such PVDF fiber-based sensors, a feasible process to prepare and extract electrodes on the surface of the fibers had to be developed. Compared with stainless steel filament-core fibers, the molybdenum filament-core PVDF fibers were easy to stretch. The molybdenum filament was then covered by a cylindrical PVDF layer with a diameter of 400 μm. One half of the longitudinal surface of the fibers was spray-coated with a conductive silver adhesive. The metal core was then used as one electrode, and the conductive silver adhesive was used as the other electrode. After polarization, a single metal-core PVDF fiber could be used as an airflow sensor. The surface structure and the sections of the PVDF fiber were analyzed by scanning electron microscopy. The results of the mechanical stretching tests showed that the metal core greatly enhanced the mechanical properties of the PVDF fibers. X-ray diffraction revealed that the greater the stretching ratio, the higher the α-to-β-phase conversion rate during the preparation of the PVDF fibers. A single metal-core PVDF fiber was used as a bionic airflow sensor, and a mechanical model of this sensor was derived. The airflow sensing capability of the PVDF fiber was experimentally confirmed in a miniature wind tunnel. The results showed that a cantilevered metal-core PVDF fiber is capable of detecting the range

Development of high performance capacitor is reaching towards new generation where the ferroelectric materials take places as the active dielectric layer. The motivation of this study is to produce high capacitance device with long life cycle. This was configured by preparing bilayered films where lead titanate as an active dielectric layer and stacked with the top dielectric layer, poly(vinyledenefluoride-trifluoroethylene). Both of them are being referred that have one in common which is ferroelectric behavior. Therefore the combination of ceramic and polymer ferroelectric material could perform optimum dielectric characteristic for capacitor applications. The fabrication was done by simple sol-gel spin coating method that being varied at spinning speed property for polymer layers, whereas maintaining the ceramic layer. The characterization of PVDF-TrFE/PbTiO3 was performed according to metal-insulator-metal stacked capacitor measurement which includes structural, dielectric, and ferroelectric measurement.

Electrospinning is a nano-scale fiber production method with various polymer materials. This technique allows simple fiber diameters control by changing the physical conditions such as applied voltage and polymer solution viscosity during the fabrication process. The electrospun polymer fibers form a thin porous film with high surface area to volume ratio. Due to these unique characteristics, it is widely used for many application fields such as photocatalyst, electric sensor, and antibacterial scaffold for tissue engineering. Filtration is one of the main applications of electrospun polymer fibers for specific application of filtering out dust particles and dehumidification. Most polymers which are commonly used in electrospinning are hard to perform the filtering and dehumidification simultaneously because of their low hygroscopic property. To overcome this obstacle, the desiccant polymers are developed such as polyacrylic acid and polysulfobetaine methacrylate. However, the desiccant polymers are generally expensive and need special solvent for electrospinning. An alternating way to solve these problems is mixing desiccant material like zeolite in polymer solution during an electrospinning process. In this study, the free surface energy characteristics of electrospun polyvinylidene fluoride (PVDF) film with various zeolite concentrations are investigated to control the hygroscopic property of general polymers. Fundamental physical property of wettability with PVDF shows hydrophobicity. The electrospun PVDF film with small weight ratio with higher than 0.1% of zeolite powder shows diminished contact angles that certifying the wettability of PVDF can be controlled using desiccant material in electrospinning process. To quantify the surface energy of electrospun PVDF films, sessile water droplets are introduced on the electrospun PVDF film surface and the contact angles are measured. The contact angles of PVDF film are 140° for without zeolite and 80° for with 5

Immobilization of glucose oxidase (GOD) within a hybrid mesoporous membrane with 12 nm pore diameter was successfully achieved, resulting in catalytically high efficiency during flow of a glucose solution across the membrane. PMID:18253526

Human LL-37 is a multifunctional cathelicidin peptide that has shown a wide spectrum of antimicrobial activity by permeabilizing microbial membranes similar to other antimicrobial peptides; however, its molecular mechanism has not been clarified. Two independent experiments revealed LL-37 bound to membranes in the {alpha}-helical form with the axis lying in the plane of membrane. This led to the conclusion that membrane permeabilization by LL-37 is a nonpore carpet-like mechanism of action. Here we report the detection of transmembrane pores induced by LL-37. The pore formation coincided with LL-37 helices aligning approximately normal to the plane of the membrane. We observed an unusual phenomenon of LL-37 embedded in stacked membranes, which are commonly used in peptide orientation studies. The membrane-bound LL-37 was found in the normal orientation only when the membrane spacing in the multilayers exceeded its fully hydrated value. This was achieved by swelling the stacked membranes with excessive water to a swollen state. The transmembrane pores were detected and investigated in swollen states by means of oriented circular dichroism, neutron in-plane scattering, and x-ray lamellar diffraction. The results are consistent with the effect of LL-37 on giant unilamellar vesicles. The detected pores had a water channel of radius 2333 {angstrom}. The molecular mechanism of pore formation by LL-37 is consistent with the two-state model exhibited by magainin and other small pore-forming peptides. The discovery that peptide-membrane interactions in swollen states are different from those in less hydrated states may have implications for other large membrane-active peptides and proteins studied in stacked membranes.

Poly(vinylidene fluoride) (PVDF) is a kind of important piezoelectric polymer used in spacecraft industry. But the atomic oxygen (AO) is the most abundant element in the low Earth orbit (LEO) environment. AO collision degradation is an important issue in the application of PVDF on spacecrafts. To investigate the erosion behaviors of PVDF during AO impacts and how to improve the stability of PVDF against AO impacts, the temperature evolution, mass loss, and erosion yields of neat PVDF, neat polyhedral oligomeric silsesquioxanes compound (3,3,3-trifluoropropyl)8Si8O12 (FP-POSS) and the PVDF/FP-POSS composite under AO impacts, as well as some key disintegrated structures and separated chemical compositions, were researched using the molecular dynamics (MD) simulations and the reactive ReaxFF force field. The simulation erosion yield result of PVDF is very close to the experiment results, which shows our simulations are reliable. The results of the temperature evolution, mass loss, and erosion yield of three materials show that the antierosion performance of PVDF is not outstanding. However, incorporating FP-POSS into PVDF matrix enhances the stability of PVDF against AO impact greatly and reduces the temperature rise, mass loss, and the erosion yield of PVDF rapidly. A detailed analysis on the flight chemical compositions and key snapshots of the structures reveals that the erosion process on PVDF and PVDF/FP-POSS is continuous and should be derived from the same PVDF matrix in two materials. In contrast, the erosion process on FP-POSS is stepped. The erosion will not take place until the number of AO reaches a specific value. There is a barrier for the erosion of high-energy AO because of the stable cagelike Si-O frame in FP-POSS molecules. This should be chiefly responsible for the high stability of FP-POSS and the reinforcement mechanism of FP-POSS on PVDF against AO impacts. This work is helpful for people to understand the erosion details of PVDF and POSS and

A zwitterionic polymer, poly(3-(methacryloylamino) propyl-dimethyl-(3-sulfopropyl) ammonium hydroxide) (poly(MPDSAH)) was successfully grafted in high density from the surface of poly(vinylidene fluoride) (PVDF) hollow fiber membrane via a two-step polymerization. Poly(2-hydroxyethyl methacrylate) (poly(HEMA)) chains were firstly grafted from outside surface of PVDFmembrane through atom transfer radical polymerization (ATRP) to provide the initiation sites for subsequent cerium (Ce (IV))-induced graft copolymerization of polyMPDSAH in the presence of N,N'-ethylene bisacrylamide (EBAA) as a cross-linking agent. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) confirmed that the EBAA could stimulate zwitterionic polymers grafting onto the membrane surface. The dense poly(MPDSAH) layers on the PVDFmembrane surface were revealed by the scanning electron microscope (SEM). The mechanical property of PVDFmembrane was improved by the zwitterionic surface layers. The gravimetry results indicated the grafting amount increased to 520 μg/cm2 for a copolymerization time of more than 3 h. Static and dynamic water contact angle measurements showed that the surface hydrophilicity of the PVDFmembranes was significantly enhanced. As the grafting amount reached 513 μg cm-2, the value of contact angle dropped to 22.1° and the amount of protein adsorption decreased to zero. The cyclic experiments for BSA solution filtration demonstrated that the extent of protein fouling was significantly reduced and most of the fouling was reversible. The grafted polymer layer on the PVDFmembrane showed a good stability during the membrane cleaning process. The experimental results concluded a good prospect in obtaining the sulfobetaine-modified PVDFmembranes with high mechanical strength, good anti-protein-fouling performance, and long-term stability via the two-step polymerization.

Electroporation increases ionic and molecular transport through cell membranes by creating transient aqueous pores. These pores cannot be directly observed experimentally, but cell system modeling with dynamic electroporation predicts pore populations that produce cellular responses consistent with experiments. We show a cell system model's response that illustrates the life cycle of a pore population in response to a widely used 1 kV/cm, 100 μs trapezoidal pulse. Rapid pore creation occurs early in the pulse, followed by the gradual emergence of a subpopulation of large pores reaching ~30 nm radius. After the pulse, pores rapidly contract to form a single thermally broadened distribution of small pores (~1 nm radius) that slowly decays. We also show the response of the same model to pulses of 100 ns to 1 ms duration, each with an applied field strength adjusted such that a total of 10,000±100 pores are created. As pulse duration is increased, the pore size distributions vary dramatically and a distinct subpopulation of large pores emerges for pulses of microsecond and longer duration. This subpopulation of transient large pores is relevant to understanding rapid transport of macromolecules into and out of cells during a pulse. PMID:24290730

Perfringolysin O (PFO) is a transmembrane (TM) β-barrel protein that inserts into mammalian cell membranes. Once inserted into membranes, PFO assembles into pore-forming oligomers containing 30–50 PFO monomers. These form a pore of up to 300 Å, far exceeding the size of most other proteinaceous pores. In this study, we found that altering PFO TM segment length can alter the size of PFO pores. A PFO mutant with lengthened TM segments oligomerized to a similar extent as wild-type PFO, and exhibited pore-forming activity and a pore size very similar to wild-type PFO as measured by electron microscopy and a leakage assay. In contrast, PFO with shortened TM segments exhibited a large reduction in pore-forming activity and pore size. This suggests that the interaction between TM segments can greatly affect the size of pores formed by TM β-barrel proteins. PFO may be a promising candidate for engineering pore size for various applications.

Perfringolysin O (PFO) is a transmembrane (TM) β-barrel protein that inserts into mammalian cell membranes. Once inserted into membranes, PFO assembles into pore-forming oligomers containing 30–50 PFO monomers. These form a pore of up to 300 Å, far exceeding the size of most other proteinaceous pores. In this study, we found that altering PFO TM segment length can alter the size of PFO pores. A PFO mutant with lengthened TM segments oligomerized to a similar extent as wild-type PFO, and exhibited pore-forming activity and a pore size very similar to wild-type PFO as measured by electron microscopy and a leakagemore » assay. In contrast, PFO with shortened TM segments exhibited a large reduction in pore-forming activity and pore size. This suggests that the interaction between TM segments can greatly affect the size of pores formed by TM β-barrel proteins. PFO may be a promising candidate for engineering pore size for various applications.« less

The multidomain pro-apoptotic Bcl-2 family proteins BAK and BAX are believed to form large oligomeric pores in the mitochondrial outer membrane during apoptosis. Formation of these pores results in the release of apoptotic factors including cytochrome c from the intermembrane space into the cytoplasm, where they initiate the cascade of events that lead to cell death. Using the site-directed spin labeling method of electron paramagnetic resonance (EPR) spectroscopy, we have determined the conformational changes that occur in BAK when the protein targets to the membrane and forms pores. The data showed that helices α1 and α6 disengage from the rest of the domain, leaving helices α2-α5 as a folded unit. Helices α2-α5 were shown to form a dimeric structure, which is structurally homologous to the recently reported BAX “BH3-in-groove homodimer.” Furthermore, the EPR data and a chemical cross-linking study demonstrated the existence of a hitherto unknown interface between BAK BH3-in-groove homodimers in the oligomeric BAK. This novel interface involves the C termini of α3 and α5 helices. The results provide further insights into the organization of the BAK oligomeric pores by the BAK homodimers during mitochondrial apoptosis, enabling the proposal of a BAK-induced lipidic pore with the topography of a “worm hole.” PMID:24337568

Poly(vinylidene fluoride) (PVDF) and PVDF copolymers are well known for their ferroelectric and piezoelectric properties. Currently, they are mainly used in applications in the form of films. Thin PVDF films have been shown to possess unique ferroelectric properties in the nanoscale range. However, their two-dimensional nature limits their applicability in active engineering materials and structures. One-dimensional PVDF nanofibers can be expected to combine ferroelectric behavior with enhanced mechanical properties and ultrahigh flexibility providing critical advantages for applications. In this work, novel continuous PVDF nanofibers were nanomanufactured and systematically studied for the first time. Nanofibers from PVDF and P(VDF-TrFE) copolymer with several molecular weights and co-polymer compositions were manufactured by electrospinning. The method consists of spinning polymer solutions in high electric fields. Effects of process parameters on nanofiber diameters and morphology were studied. Resulting nanofibers were characterized by FE-SEM, TEM, XRD, FTIR, DSC and TGA. Effects of annealing on copolymer nanofibers were analyzed. Nanofiber-reinforced composites were manufactured and their polarization behavior studied using a specially designed experimental device. A number of pioneering observations and discoveries were made as a result of this analysis. For example, analysis of crystalline structure of PVDF nanofibers showed that the initial a phase of the PVDF raw material was converted to beta phase during electrospinning. This result is very encouraging as the beta phase is primarily responsible for the piezo- and ferroelectric behavior of PVDF polymers. It was also shown for the first time that nanofabricated P(VDF-TrFE) nanofibers exhibited distinct Curie points and different structures than their raw materials. Annealing was shown to be an effective way to modify properties of P(VDF-TrFE) co-polymer nanofibers. Overall, the results demonstrated for the

Cerium(III)-N,N-dimethylformamide-bisulfate [Ce(DMF)(HSO4)3] complex is doped into poly(vinylidene fluoride) (PVDF) to induce a higher yield (99%) of the electroactive phases (β- and γ-phases) of PVDF. A remarkable enhancement of the output voltage (∼32 V) of a nanogenerator (NG) based on a nonelectrically poled cerium(III) complex containing PVDF composite film is achieved by simple repeated human finger imparting, whereas neat PVDF does not show this kind of behavior. This high electrical output resembles the generation of self-poled electroactive β-phase in PVDF due to the electrostatic interactions between the fluoride of PVDF and the surface-active positive charge cloud of the cerium complex via H-bonding and/or bipolar interaction among the opposite poles of cerium complex and PVDF, respectively. The capacitor charging capability of the flexible NG promises its applicability as piezoelectric-based energy harvester. The cerium(III) complex doped PVDF composite film exhibit an intense photoluminescence in the UV region, which might be due to a participation of electron cloud from negative pole of bipolarized PVDF. This fact may open a new area for prospective development of high-performance energy-saving flexible solid-state UV light emitters. PMID:25523039

Electrically poled poly(vinylidene fluoride) (PVDF) and polycarbonate (PC) multilayer films can be considered as a polymer electret, which stores quasi-permanent charges (i.e., ions) at PVDF/PC interfaces. In this study, the corresponding dielectric properties of electrically poled PVDF/PC multilayer films are investigated experimentally. First, the bipolar hysteresis loop becomes narrower for the poled PVDF/PC multilayer films upon increasing the poling time, because the impurity ions in PVDF are locked at the PVDF/PC interfaces. Second, asymmetric DC conductivity in poled PVDF/PC multilayer films is observed because of the pre-existing electric field in the electret layers. When the pre-existing field is in the same direction of the applied external field, enhanced DC conductivity is observed in the leakage current measurement. In contrast, if the pre-existing field is opposite to the applied external field, decreased DC conductivity is seen. More experimental evidence of polarized charge at the PVDF/PC interfaces in poled PVDF/PC multilayer films is also manifested by thermally stimulated depolarization current (TSDC) experiments.

The nuclear envelope is a double membrane structure that separates the eukaryotic cytoplasm from the nucleoplasm. The nuclear pores embedded in the nuclear envelope are the sole gateways for macromolecular trafficking in and out of the nucleus. The nuclear pore complexes assembled at the nuclear pores are large protein conglomerates composed of multiple units of about 30 different nucleoporins. Proteins and RNAs traffic through the nuclear pore complexes, enabled by the interacting activities of nuclear transport receptors, nucleoporins, and elements of the Ran GTPase cycle. In addition to directional and possibly selective protein and RNA nuclear import and export, the nuclear pore gains increasing prominence as a spatial organizer of cellular processes, such as sumoylation and desumoylation. Individual nucleoporins and whole nuclear pore subcomplexes traffic to specific mitotic locations and have mitotic functions, for example at the kinetochores, in spindle assembly, and in conjunction with the checkpoints. Mutants of nucleoporin genes and genes of nuclear transport components lead to a wide array of defects from human diseases to compromised plant defense responses. The nuclear envelope acts as a repository of calcium, and its inner membrane is populated by functionally unique proteins connected to both chromatin and—through the nuclear envelope lumen—the cytoplasmic cytoskeleton. Plant nuclear pore and nuclear envelope research—predominantly focusing on Arabidopsis as a model—is discovering both similarities and surprisingly unique aspects compared to the more mature model systems. This chapter gives an overview of our current knowledge in the field and of exciting areas awaiting further exploration. PMID:22303264

A device according to one embodiment includes a porous membrane having a surface charge and pore configuration characterized by a double layer overlap effect being present in pores of the membrane, where the porous membrane includes functional groups that preferentially interact with either cations or anions. A device according to another embodiment includes a porous membrane having a surface charge in pores thereof sufficient to impart anion or cation selectivity in the pores. Additional devices, systems and methods are also presented.

Functionalized polymer materials with ion exchange groups and integration of nano-structured materials is an emerging area for catalytic and water pollution control applications. The polymerization of materials such as acrylic acid often requires persulfate initiator and a high temperature start. However, is generally known that metal ions accelerate such polymerizations starting from room temperature. If the metal is properly selected, it can be used in environmental applications adding two advantages simultaneously. This paper deals with this by polymerizing acrylic acid using iron as accelerant and its subsequent use for nanoparticle synthesis in hydrogel and PVDFmembranes. Characterizations of hydrogel, membranes and nanoparticles were carried out with different techniques. Nanoparticles sizes of 30–60 nm were synthesized. Permeability and swelling measurements demonstrate an inverse relationship between hydrogel mesh size (6.30 to 8.34 nm) and membranepores (222 to 110 nm). Quantitative reduction of trichloroethylene/chloride generation by Fe/Pd nanoparticles in hydrogel/membrane platforms was also performed. PMID:24954975

Formation of the nuclear pore is an intricate process involving membrane fusion and the ordered assembly of up to 1,000 pore proteins. As such, the study of pore assembly is not a simple one. Interestingly, annulate lamellae, a cytoplasmic organelle consisting of stacks of flattened membrane cisternae perforated by numerous pore complexes, have been found to form spontaneously in a reconstitution system derived from Xenopus egg extracts, as determined by electron microscopy (Dabauvalle et al., 1991). In this work, a biochemical assay for annulate lamellae (AL) formation was developed and used to study the mechanism of AL assembly in general and the assembly of individual nucleoporins into pore complexes in particular. Upon incubation of Xenopus egg cytosol and membrane vesicles, the nucleoporins nup58, nup60, nup97, nup153, and nup200 initially present in a disassembled form in the cytosol became associated with membranes and were pelletable. The association was time and temperature dependent and could be measured by immunoblotting. Thin-section electron microscopy as well as negative staining confirmed that annulate lamellae were forming coincident with the incorporation of pore proteins into membranes. Homogenization and subsequent flotation of the membrane fraction allowed us to separate a population of dense membranes, containing the integral membranepore protein gp210 and all other nucleoporins tested, from the bulk of cellular membranes. Electron microscopy indicated that annulate lamellae were enriched in this dense, pore protein-containing fraction. GTP gamma S prevented incorporation of the soluble pore proteins into membranes. To address whether AL form in the absence of N-acetylglucosaminylated pore proteins, AL assembly was carried out in WGA-sepharose-depleted cytosol. Under these conditions, annulate lamellae formed but were altered in appearance. When the membrane fraction containing this altered AL was homogenized and subjected to flotation, the

This paper presents a new additive manufacturing (AM) process to directly and continuously print piezoelectric devices from polyvinylidene fluoride (PVDF) polymeric filament rods under a strong electric field. This process, called ‘electric poling-assisted additive manufacturing or EPAM, combines AM and electric poling processes and is able to fabricate free-form shape piezoelectric devices continuously. In this process, the PVDF polymer dipoles remain well-aligned and uniform over a large area in a single design, production and fabrication step. During EPAM process, molten PVDF polymer is simultaneously mechanically stresses in-situ by the leading nozzle and electrically poled by applying high electric field under high temperature. The EPAM system was constructed to directly print piezoelectric structures from PVDF polymeric filament while applying high electric field between nozzle tip and printing bed in AM machine. Piezoelectric devices were successfully fabricated using the EPAM process. The crystalline phase transitions that occurred from the process were identified by using the Fourier transform infrared spectroscope. The results indicate that devices printed under a strong electric field become piezoelectric during the EPAM process and that stronger electric fields result in greater piezoelectricity as marked by the electrical response and the formation of sharper peaks at the polar β crystalline wavenumber of the PVDF polymer. Performing this process in the absence of an electric field does not result in dipole alignment of PVDF polymer. The EPAM process is expected to lead to the widespread use of AM to fabricate a variety of piezoelectric PVDF polymer-based devices for sensing, actuation and energy harvesting applications with simple, low cost, single processing and fabrication step.

In this work, we fabricate an omniphobic microporous membrane for membrane distillation (MD) by modifying a hydrophilic glass fiber membrane with silica nanoparticles followed by surface fluorination and polymer coating. The modified glass fiber membrane exhibits an anti-wetting property not only against water but also against low surface tension organic solvents that easily wet a hydrophobic polytetrafluoroethylene (PTFE) membrane that is commonly used in MD applications. By comparing the performance of the PTFE and omniphobic membranes in direct contact MD experiments in the presence of a surfactant (sodium dodecyl sulfate, SDS), we show that SDS wets the hydrophobic PTFE membrane but not the omniphobic membrane. Our results suggest that omniphobic membranes are critical for MD applications with feed waters containing surface active species, such as oil and gas produced water, to prevent membranepore wetting.

Direct contact membrane distillation process has been studied using microporous polytetrafluoroethylene and polyvinylidene fluoride membranes. The membranes were characterized in terms of their non-wettability, pore size distribution and porosity. The mean pore sizes and pore size distributions were obtained by means of wet/dry flow method. The mean pore size and the effective porosity of the membranes were also determined from the gas permeation test. A theoretical model that considers the pore size distribution together with the gas transport mechanisms through the membranepores was developed for this process. The contribution of each mass transport mechanism was analyzed. It was found that both membranes have pore size distributions in the Knudsen region and in the transition between Knudsen and ordinary diffusion region. The transition region was the major contribution to mass transport. The predicted water vapor permeability of the membranes were compared with the experimental ones. The effect of considering pore size distribution instead of mean pore size to predict the water vapor permeability of the membranes was investigated.

Background. Morphological characterization of hemodialysis membranes is necessary to improve pore design. Aim. To delineate membranepore structure of a high flux filter, Polyflux 210H. Methods. We used a Joel JSM-6010LV scanning electron microscope (SEM) and a SU6600 Hitachi field emission scanning electron microscope (FESEM) to characterize the pore and fiber morphology. The maximal diameters of selected uremic toxins were calculated using the macromolecular modeling Crystallographic Object-Oriented Toolkit (COOT) software. Results. The mean pore densities on the outermost and innermost surfaces of the membrane were 36.81% and 5.45%, respectively. The membrane exhibited a tortuous structure with poor connection between the inner and outer pores. The aperture's width in the inner surface ranged between 34 and 45 nm, which is 8.76–11.60 times larger than the estimated maximum diameter of β2-microglobulin (3.88 nm). Conclusion. The results suggest that the diameter size of inner pore apertures is not a limiting factor to middle molecules clearance, the extremely diminished density is. Increasing inner pore density and improving channel structure are strategies to improve clearance of middle molecules. PMID:23209902

A novel β-phase polyvinylidene difluoride (PVDF) nanofibrous membrane decorated with multiwalled carbon nanotubes (MWCNTs) and platinum nanoparticles (PtNPs) was fabricated by an improved electrospinning technique. The morphology of the fabricated PVDF-MWCNT-PtNP nanofibrous membrane was observed by scanning electron microscopy, and the formation of high β-phase in the hybrid nanofibrous membrane was investigated by Fourier transform infrared spectroscopy and differential scanning calorimetry. The uniform dispersion of MWCNTs and PtNPs in the PVDF hybrid nanofibrous membrane and their interaction were explored by transmission electron microscopy and X-ray diffraction. For the first time, we utilized this created PVDF-MWCNT-PtNP nanofibrous membrane for biosensor and catalysis applications. The nonenzymatic amperometric biosensor with highly stable and sensitive, and selective detection of both H2O2 and glucose was successfully fabricated based on the electrospun PVDF-MWCNT-PtNP nanofibrous membrane. In addition, the catalysis of the hybrid nanofibrous membrane for oxygen reduction reaction was tested, and a good catalysis performance was found. We anticipate that the strategies utilized in this work will not only guide the further design of functional nanofiber-based biomaterials and biodevices but also extend the potential applications in energy storage, cytology, and tissue engineering. PMID:24754739

We simulate molecular transport in elongated hydrothermal pore systems influenced by a thermal gradient. We find extreme accumulation of molecules in a wide variety of plugged pores. The mechanism is able to provide highly concentrated single nucleotides, suitable for operations of an RNA world at the origin of life. It is driven solely by the thermal gradient across a pore. On the one hand, the fluid is shuttled by thermal convection along the pore, whereas on the other hand, the molecules drift across the pore, driven by thermodiffusion. As a result, millimeter-sized pores accumulate even single nucleotides more than 108-fold into micrometer-sized regions. The enhanced concentration of molecules is found in the bulk water near the closed bottom end of the pore. Because the accumulation depends exponentially on the pore length and temperature difference, it is considerably robust with respect to changes in the cleft geometry and the molecular dimensions. Whereas thin pores can concentrate only long polynucleotides, thicker pores accumulate short and long polynucleotides equally well and allow various molecular compositions. This setting also provides a temperature oscillation, shown previously to exponentially replicate DNA in the protein-assisted PCR. Our results indicate that, for life to evolve, complicated active membrane transport is not required for the initial steps. We find that interlinked mineral pores in a thermal gradient provide a compelling high-concentration starting point for the molecular evolution of life. PMID:17494767

In this work, PANI:PVDF composites films were prepared with different PANI contents (p = 1, 2, 3, 4 and 5%). The resulting films were dried at various temperatures such as 30, 90 and 120 °C. The alternating current mechanisms and dielectric relaxation and of PANI:PVDF films were studied using complex impedance spectroscopy over a wide range of temperature (303-453 K) and a frequency range (1 kHz to 1 MHz). We found that the ac conductivity in PANI:PVDF composite is governed by correlated barrier hopping (CBH) model. In dielectric loss modulus study, two relaxation processes were identified. The first peak was associated to Maxwell Wagner-Sillas (MWS) relaxation whereas the second one which obtained at higher frequency was attributed to the αc relaxation. For PANI:PVDF film which dried at 30 °C, the MWS relaxation appears only at higher temperature. The temperature dependence of αc relaxation was suitably fitted according to Vogel Flucher Temman model whereas MWS relaxation follows Arrhenius type behavior. The effect of drying temperature on microstructure and phase crystallization of PVDF in the composites was carried out using atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. These results were used to find a reasonable correlation between microstructure and electrical properties.

A robust wear/corrosion-resistant superhydrophobic polyvinylidene fluoride (PVDF)/fluorinated ethylene propylene (FEP)/carbon nanofibers (CNFs) composite coating with a water contact angle (WCA) of 164 ± 1.5° and a slide angle of 5 ± 0.2° has been fabricated through the combination of chemical etching and spraying technique. The WCA of the coating still maintains 141 ± 1.2° after 10,000 times rubbing due to the designed internal nano/micro-structure and the slide angle increases from 5 ± 0.2° to 20 ± 0.5°. The prepared coating also demonstrates excellent corrosion-resistance property under strongly acidic or alkaline conditions for 15 days. The wear-resistance of the superhydrophobic coating is approximately 5 times higher than the pure PVDF coating and commercial fluorocarbon coating. These excellent mechanical properties are attributed to the new groups of Cdbnd C and Csbnd C by dehydrofluorination of PVDF and the new β-phase of PVDF by recrystallization of the α-phase. Furthermore, the enhanced adhesive ability of the coating corresponds with Grade 1 according to GB/T9286, mainly because that the interaction force among PVDF macromolecules can be intensified by chemical cross-linking and the hydroxyl groups formed on the surface of the aluminum plate by etching. It is believed that this robust multifunctional superhydrophobic coating may have the potential values in large-scale application.

Nanoscale ordering in a polymer blend structure is indispensable to obtain materials with tailored properties. It was established here that controlling the arrangement of nanoparticles, with different characteristics, in co-continuous PC/PVDF (polycarbonate/poly(vinylidene fluoride)) blends can result in outstanding microwave absorption (ca. 90%). An excellent reflection loss (RL) of ca. -71 dB was obtained for a model blend structure wherein the conducting (multiwall carbon nanotubes, MWNTs) and the magnetic inclusions (Fe3O4) are localized in PVDF and the dielectric inclusion (barium titanate, BT) is in PC. The MWNTs were modified using polyaniline, which facilitates better charge transport in the blends. Furthermore, by introducing surface active groups on BT nanoparticles and changing the macroscopic processing conditions, the localization of BT nanoparticles can be tailored, otherwise BT nanoparticles would localize in the preferred phase (PVDF). In this study, we have shown that by ordered arrangement of nanoparticles, the incoming EM radiation can be attenuated. For instance, when PANI-MWNTs were localized in PVDF, the shielding was mainly through reflection. Now by localizing the conducting inclusion and the magnetic lossy materials in PVDF and the dielectric materials in PC, an outstanding shielding effectiveness of ca. -37 dB was achieved where shielding was mainly through absorption (ca. 90%). Thus, this study clearly demonstrates that lightweight microwave absorbers can be designed using polymer blends as a tool. PMID:26431367